Device and method for controlling power amplifier

ABSTRACT

A control device provides a supply voltage to an output transistor of a power amplifier. The control device includes a detector encoder, a switch sequencer and a power switch. The detector encoder receives a detection signal indicating a negative peak voltage level of an output signal of the power amplifier, receives a reference signal indicating a critical voltage of the detection signal at which the negative peak voltage level of the output transistor is deemed to be out of voltage with reference to saturation voltage of the output transistor, compares the detection and reference signals, and outputs Boost Request and Recovery Request signals in response. The switch sequencer translates the Boost Request and Recovery Request signals into multiple control bits. The power switch coordinates switching among a no boost voltage and multiple boost voltages based on the control bits, and outputs one of these voltages as the supply voltage.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application under 37 C.F.R.§1.53(b) of U.S. patent application Ser. No. 13/834,953 filed on Mar.15, 2013. Priority under 35 U.S.C. §120 is claimed from U.S. patentapplication Ser. No. 13/834,953, and the entire disclosure of U.S.patent application Ser. No. 13/834,953 is specifically incorporatedherein by reference.

BACKGROUND

Wireless communications systems are designed around various modulationschemes, such as orthogonal frequency-division multiplexing (OFDM) andcode division multiple access (CDMA), intended to provide efficientutilization of the allocated spectrum. Spectrally efficient modulationschemes have high crest factors (e.g., peak to average power ratios).However, proper conveyance of data and acceptable spectral re-growthcharacteristics place a linearity burden on the transmit chain,including a power amplifier.

In order to achieve the required linearity, conventional systemstypically require substantial power back-off from saturation of anoutput transistor in the power amplifier, which significantly reducesefficiency. In portable equipment, such as cellular telephones,reduction in efficiency translates into shorter battery life and reducedoperating time between battery recharges. Generally, the industry trendis to increase the interval between battery recharges and/or to decreasethe size of the batteries. Therefore, the efficiency of power amplifiersshould be increased while still meeting linearity requirements.

Attempts have been made to improve linearity focusing on providing twolevels of drain (or collector) supply voltages. For example, U.S. Pat.No. 8,174,313 to Vice, issued May 8, 2012, which is hereby incorporatedby reference, discloses controlling a power amplifier using a detector,configured to detect the power level of a radio frequency (RF) inputsignal with respect to a predetermined power threshold and a controllerconfigured to provide a supply voltage to the power amplifier inresponse to a detection signal from the detector. The supply voltage haseither a low voltage value when the detection signal indicates that thepower level is below the power threshold, or a high (boosted) voltagevalue when the detection signal indicates that the power level is abovethe power threshold. However, greater efficiency and simpler design aredesirable.

SUMMARY

In a representative embodiment, a device for controlling operation of apower amplifier configured to amplify an input signal includes adetector and a controller. The detector is configured to detect avoltage level of an output signal of the power amplifier with respect toa predetermined boost threshold and to generate a correspondingdetection signal and a reference signal. The controller is configured toprovide a supply voltage to an output transistor of the power amplifierbased on a comparison of the detection signal and the reference signal,the supply voltage being a no boost voltage, which is substantially thesame as a supply voltage, when the comparison indicates that the voltagelevel is within the predetermined boost threshold. The supply voltage isone of a plurality of boost voltages when the detection signal indicatesthat the voltage level is beyond the predetermined boost threshold. Thecontroller generates the plurality of boost voltages by boosting thesupply voltage.

In another representative embodiment, a method is provided forselectively boosting a collector supply voltage of an output transistorin a power amplifier amplifying a radio frequency (RF) signal. Themethod includes providing a supply voltage as the collector supplyvoltage of the output transistor by connecting a supply voltage sourceto the output transistor, and selectively connecting a plurality ofcharge storage capacitors to receive charge from the supply voltagesource to charge each of the plurality of charge storage capacitors to acapacitor voltage value; evaluating a magnitude of an envelope of the RFsignal and detecting when a lowest occurring voltage extreme of theenvelope becomes less than a predetermined boost threshold; providing afirst boosted voltage as the collector supply voltage when the lowestoccurring voltage extreme of the envelope becomes less than thepredetermined boost threshold by connecting one of the plurality ofcharge storage capacitors between the supply voltage source and theoutput transistor, the first boosted voltage including the supplyvoltage plus the capacitor voltage value previously stored in one of theplurality of charge storage capacitors; and providing a second boostedvoltage as the collector supply voltage when the lowest occurringvoltage extreme of the envelope again becomes less than thepredetermined boost threshold by simultaneously connecting two of theplurality of charge storage capacitors between the supply voltage sourceand the output transistor, the second boosted voltage including thecapacitor voltage values previously stored in both of the two chargestorage capacitors.

In another representative embodiment, a device for controlling operationof a power amplifier configured to amplify an RF signal includes adetector, a DC controller and a compensation circuit. The detector isconfigured to generate a detection signal and a reference signal basedon a negative peak voltage level of an output signal of the poweramplifier. The DC controller is configured to provide a DC supplyvoltage and compensation signals to an output transistor of the poweramplifier based on comparison of the detection signal and the referencesignal, the DC supply voltage being a no boost voltage when the negativepeak voltage level is above a predetermined boost threshold, and one ofa medium boost voltage and a high boost voltage when the negative peakvoltage level is below the predetermined boost threshold. Thecompensation circuit includes a plurality of series RC circuitsconnected in series with a corresponding plurality of switches forselectively connecting one or more of the plurality of series RCcircuits, respectively, around the transistor in a shunt-shunt feedbackconfiguration in response to the plurality of compensation signals.

BRIEF DESCRIPTION OF THE DRAWINGS

The example embodiments are best understood from the following detaileddescription when read with the accompanying drawing figures. It isemphasized that the various features are not necessarily drawn to scale.In fact, the dimensions may be arbitrarily increased or decreased forclarity of discussion. Wherever applicable and practical, like referencenumerals refer to like elements.

FIG. 1 is a block diagram illustrating an amplifier control circuit,according to a representative embodiment.

FIG. 2 is a circuit diagram illustrating an output transistorcompensation control circuit for correcting quiescent bias increase inthe power amplifier shown in FIG. 1, according to a representativeembodiment.

FIG. 3 is a block diagram illustrating a detector of the amplifiercontrol circuit shown in FIG. 1, according to a representativeembodiment.

FIG. 4 is a block diagram illustrating a DC controller of the amplifiercircuit, according to a representative embodiment.

FIG. 5 is a circuit diagram of a detector bias circuit, together withthe power amplifier stage and the detector, according to arepresentative embodiment.

FIG. 6 is a block diagram illustrating a detector encoder of the DCcontroller, according to a representative embodiment.

FIG. 7 is a circuit diagram illustrating a switch sequencer of the DCcontroller, according to a representative embodiment.

FIG. 8 is a circuit diagram illustrating a power switch of the DCcontroller, according to a representative embodiment.

FIG. 9A is a logic circuit diagram of a clock encoder of the switchsequencer, according to a representative embodiment.

FIG. 9B is a circuit diagram showing an inverter of the clock encoder710, according to a representative embodiment.

FIG. 10 is a circuit diagram of an x-encoder of the switch sequencer,according to a representative embodiment.

FIG. 11A is a circuit diagram of an abc-encoder of the switch sequencer,according to a representative embodiment.

FIG. 11B is a logic circuit diagram of an SR-latch in the abc-encoder,according to a representative embodiment.

FIG. 12 is a circuit diagram of w-encoder of the switch sequencer,according to a representative embodiment.

FIG. 13A is a logic circuit diagram of a fault recovery circuit of theDC controller, according to a representative embodiment.

FIG. 13B is a circuit diagram of a slow rise NOR gate of the faultrecovery circuit of the DC controller 130, according to a representativeembodiment.

FIG. 13C is a circuit diagram of a slow fall inverter of the faultrecovery circuit of the DC controller, according to a representativeembodiment.

FIG. 14 is a logic circuit diagram of a compensation circuit of theswitch sequencer, according to a representative embodiment.

FIG. 15 is a block diagram of a driver decoder of the switch sequencer,according to a representative embodiment.

FIG. 16 is a logic circuit diagram of a d-encoder of the driver decoder,according to a representative embodiment.

FIG. 17 is a logic circuit diagram of a multiplexer of the driverencoder, according to a representative embodiment.

FIG. 18 is a circuit diagram of a charge manager of the driver decoder,according to a representative embodiment.

FIG. 19 is a circuit diagram of an S1clk-encoder of the switchsequencer, according to a representative embodiment.

FIG. 20 is a circuit diagram of an n-sequencer of the driver decoder,according to a representative embodiment.

FIG. 21 is a circuit diagram of a p-sequencer of the driver decoder,according to a representative embodiment.

FIG. 22 is a circuit diagram of a charge pump voltage source of the DCcontroller, according to a representative embodiment.

FIG. 23 is a circuit diagram illustrating a compensation feedback switchof the output transistor compensation control circuit, according to arepresentative embodiment.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation andnot limitation, representative embodiments disclosing specific detailsare set forth in order to provide a thorough understanding of thepresent teachings. However, it will be apparent to one having ordinaryskill in the art having had the benefit of the present disclosure thatother embodiments according to the present teachings that depart fromthe specific details disclosed herein remain within the scope of theappended claims. Moreover, descriptions of well-known apparatuses andmethods may be omitted so as to not obscure the description of therepresentative embodiments. Such methods and apparatuses are clearlywithin the scope of the present teachings.

An envelope tracking technique may be used to improve amplifierefficiency. Generally, a collector supply voltage provided to the outputtransistor of a power amplifier (or drain supply voltage, depending onthe type of output transistor incorporated in the power amplifier) ismodulated to provide the output transistor the voltage required by thecarrier envelope at each point in time, but no more. In comparison,whereas a traditional power amplifier may provide 3.3V to the collectorof the output transistor at all times, the envelope tracking techniqueaccording to various embodiments provides real time optimization of thecollector supply voltage using at least three predetermined voltages, sothat the collector supply voltage is sufficient, but not excessive, atall times. The envelope tracking technique therefore enhancesefficiency, particularly at times when the carrier envelope is belowmaximum.

Conventional envelope tracking techniques involve a linear trackingvoltage supply, which is modulated by an envelope detector. Such asystem is cumbersome, however, because it includes a continuouslyvariable DC-to-DC converter, which typically requires a large high-Qinductor.

According to various embodiments, an envelope tracking technique isprovided that requires no continuously variable DC-to-DC converter.Rather, the collector supply voltage (or drain supply voltage) providedto the output transistor of the power amplifier is adjusted to be one ofat least three values, depending on the envelope of the carrier of an RFinput signal Vin, to ensure that the output transistor has sufficientcollector supply voltage required by the carrier envelope. For example,the three collector supply voltages may be one of a no boost voltage Vnb(supply voltage, e.g., provided by a battery), medium boost voltage Vmbthat is about one and a half times the no boost voltage, and high boostvoltage Vhb that is about twice the no boost voltage. Alternativeembodiments contemplate more than three collector supply voltages (morethan two boost voltage steps, or alternatively, a combination of booststeps and fractionated voltage steps, that is, voltage steps below thebattery voltage). Selective application of the boosted voltages to thecollector of the output transistor enables the output transistor tocontinue to operate properly when maximum power output is required.

FIG. 1 is a block diagram illustrating an amplifier control circuit,according to a representative embodiment.

Referring to FIG. 1, amplifier circuit 100 includes power amplifier 110,detector 120, and DC controller 130. The power amplifier 110 isconfigured to amplify an RF input signal Vin received by the amplifiercircuit 100 through signal input port 101, and to output an amplified RFoutput signal Vout from signal output port 102. The detector 120 may bea negative peak detector, for example, for detecting negative peaks ofthe RF output signal Vout. The DC controller 130 is configured toprovide DC supply voltage Vdc having one of multiple voltage values(e.g., three voltage values), as discussed below, and one or morecompensating voltages (e.g., first and second compensation signalsComp1, Comp2).

FIG. 2 is a circuit diagram illustrating an output transistorcompensation control circuit for correcting quiescent bias increase inthe amplifier shown in FIG. 1, according to a representative embodiment.

Referring to FIG. 2, the power amplifier 110 includes an inductor 115and an output transistor 118, which may be an NPN doped bipolar junctiontransistor (BJT), for example. The collector of the output transistor118 is connected to the DC supply voltage Vdc through the inductor 115.The collector of the output transistor 118 may be connected to the DCsupply voltage Vdc through a transmission line, or through other meansof bias connection typical to the art. Other types of transistors withinthe purview of one of ordinary skill in the art may be incorporated intothe power amplifier 110, without departing from the scope of the presentteachings. For example, the output transistor 118 may be a field effecttransistor (FET), such as a gallium arsenide FET (GaAs FET), ametal-oxide semiconductor FET (MOSFET) or a heterostructure FET (HFET),a high electron mobility transistor (HEMT), a pseudomorphic HEMT(pHEMT), or the like. In the depicted embodiment, the output transistor118 includes a base connected to the signal input port 101 (not shown)for receiving the RF input signal Vin, a collector connected to a supplyoutput of the DC controller 130 for receiving a DC supply voltage Vdcvia the first inductor 115, and an emitter connected to ground. Anotherinductor (not shown) may be connected in series between the collector ofthe output transistor 118 and the signal output port 102 for outputtingthe output signal Vout of the amplifier circuit 100. Also, anothercapacitor (not shown) may be connected between the signal output port102 and ground. The additional inductor and capacitor form arepresentative output impedance matching network that is typical to theart.

For purposes of discussion, terms typically corresponding to BJTs, suchas emitter, collector and base, are used herein to describe the outputtransistor 118 of the power amplifier 110. However, it is understoodthat these terms are not intended to be limiting, and that termscorresponding to FETs, such as drain, source and gate, would beapplicable for other types of transistors in various alternativeconfigurations.

Rather than using a complex attenuator somewhere in the gain chain tocompensate for changes in S₂₁ magnitude and phase when the DC supplyvoltage Vdc is increased, a feedback network is placed around the outputtransistor 118. The feedback network generally includes a series RCcircuit comprising a resistor and a capacitor (e.g., resistor 242 andcapacitor 243) connected in series with a switch (e.g., compensationfeedback switch 240), the state of which is controlled by the DCcontroller 130 via first compensation signal Comp1. There are n−1 suchfeedback networks for an amplifier circuit 100 having a DC controller130 that produces n different output voltages. Superior neutralizationof the transfer function of the output transistor 118 shifts withrespect to the DC supply voltage Vdc has been observed with this type ofcompensation.

More particularly, the compensation control circuit 200 in FIG. 2provides a combination of feedback compensation and quiescent biascompensation, which corrects the quiescent bias increase with increasedcollector (drain) supply voltage of the output transistor 118. Thecompensation control circuit 200 includes a first current mirror 220 andsecond current mirror 230 driven by control logic that also controlscompensation feedback switches, indicated by representative compensationfeedback switch 240. The first current mirror 220 is formed by theoutput transistor 118 and mirror transistor 218, having bases connectedthrough resistor 212. The mirror transistor 218 thus forms a simplecurrent mirror representation of the bias circuit for the outputtransistor 118. The base of the output transistor 118 is also connectedto the compensation feedback switch 240.

The second current mirror 230 is formed by the mirror transistors 221and 222, having bases connected to one another. The collector of themirror transistor 222 is connected to voltage source Vbias throughresistor 224. The collector of the mirror transistor 221 is connected tothe common base of transistors 221 and 222. The collector is alsoconnected to the compensation voltage Comp through resistor 212, alsoreceived from the DC controller 130. Comp is also connected to a controlinput of the compensation feedback switch 240. A second input of thecompensation feedback switch 240 is connected to the base of the outputtransistor 118 through resistor 242 and capacitor 243. Accordingly, thecompensation feedback switch 240 is able to selectively connect ordisconnect the base of the output transistor 118 to resistor 242.

In an embodiment, the compensation feedback switch 240 (and any othercompensation feedback switches in the compensation control circuit 200)may be implemented using BJTs. FIG. 23 is a circuit diagram illustratinga BJT compensation feedback switch of the output transistor compensationcontrol circuit, according to a representative embodiment.

Referring to FIG. 23, the compensation feedback switch 240 includes afirst compensation switching transistor 1031, a second compensationswitching transistor 1032, and a compensation current source 1033. Thefirst compensation transistor 1031 includes a base connected to thecompensation switch current source 1033, a collector connected to thesignal input port 101 of the amplifier circuit 100, for example, and anemitter connected to the compensation switch current source 1033 and theemitter of the second compensation transistor 1032. In variousalternative configurations, the compensation feedback switch 240 neednot be connected to the signal input port 101. For example, thecompensation feedback switch 240 may be connected between the RC circuitand the collector of the output transistor 118, and the other end of theRC circuit may have a permanent connection to the base of the outputtransistor 118. Additionally, the base of the output transistor 1188 maynot be necessarily be directly connected to the signal input port 101,as there may be an intervening matching network. The second compensationtransistor 1032 includes a base connected to the compensation switchcurrent source 1033, a collector connected to the collector of theoutput transistor 118 (e.g., via resistor 242 and capacitor 243), and anemitter connected to a common node with the compensation switch currentsource 1033 and the emitter of the first compensation transistor 1031.The compensation switch current source 1033 may be realized as a firstresistor connected from the common base of the first and secondcompensation transistors 1031 and 1032 to the compensation controlvoltage Comp, and a second resistor connected from the common emitter ofthe first and second compensation transistors 1031 and 1032 and ground,for example.

As noted above, although the illustrative configuration is shown of thecompensation feedback switch 240, the example also applies to othercompensation feedback switches, such as compensation feedback switch 250in FIG. 4. Of course, in alternative embodiments, the compensationfeedback switch 204 (and any other compensation feedback switches in thecompensation control circuit 200) may be implemented using FETs, aswould be apparent to one of ordinary skill in the art.

As mentioned above, although not shown in FIG. 2, the number ofcompensation feedback switches and corresponding RC circuits, such ascompensation feedback switch 240, the resistor 242 and the capacitor243, is equal to one less than the number of values of the DC supplyvoltage Vdc output by the DC controller 130 (e.g., n=3 for three supplyvoltage values). However, for ease of explanation, the DC controller 130in the present example is assumed to produce only two voltages (e.g.,n=2 for two values of the DC supply voltage Vdc−Vdd and 2Vdd), so thereis only one feedback network including the compensation feedback switch240, the resistor 242 and the capacitor 243. The compensation feedbackswitch 240 is controlled by the compensation voltage Comp, which comesfrom the DC controller 130 and is configured so that the compensationfeedback switch 240 closes in the high voltage state. For instance, whenthe value of DC supply voltage Vdc is equal to 2Vdd, the compensationvoltage Comp is equal to Vdd and the compensation feedback switch 240 isclosed. The second current mirror 230 forms the bias compensationnetwork. When the compensation voltage Comp is high, the biascompensation network steals current from the resistor 224, which reducesthe drain current in the output transistor 118 sufficiently to match thequiescent current with that of the low drain supply voltage state. Forlarger values of n, the feedback and bias networks are multiplied n−1times, wherein each network has a different and optimal value for R andC. In some cases one or more resistor values may be 0 ohms. The networksare turned on successively and cumulatively with increasing DC supplyvoltages Vdc, with the result that the quiescent current ands-parameters of the output transistor 118 remain stationary with respectto the value (state) of the DC supply voltage Vdc.

Together with compensation control signal Comp from the DC controller130 (discussed below), the compensation control circuit 200 providesmore precise compensation (e.g., particularly when a FET is used as theamplifying output transistor 118) than would be obtained if feedbackcompensation alone were used. Generally, compensation refers totechniques used to maintain transfer characteristics of the outputtransistor 118 as the DC supply voltage is switched between the variousvalues provided by the DC controller 130.

FIG. 3 is a block diagram illustrating a detector of the amplifiercontrol circuit shown in FIG. 1, according to a representativeembodiment. More particularly, FIG. 3 depicts the amplifier 110 and thedetector 120, according to a representative embodiment.

Generally, the detector 120 is a temperature compensated envelopenegative peak detector. Means of temperature compensating the detector120 has been developed in keeping with the inherent sensitivity of theamplifier circuit 100 to detector error. The means involves the use of areplica diode and a special bias circuit that ensures equal bias on eachdiode. The replica diode is connected to a voltage source that issubstantially equal to the critical collector (drain) voltage of theoutput transistor 118, referred to as saturation voltage (Vsat), atwhich the DC controller 130 is expected to switch to the next highervalue of the DC supply voltage Vdc. Thus, there is a convenient way toset the aggressiveness of the amplifier circuit 100 in terms ofefficiency-linearity tradeoff by setting the value of Vsat.

Referring to FIG. 3, the amplifier 110 includes the output transistor118 and the inductor 115, as discussed above. In the depictedillustrative configuration, the detector 120 includes detector diode121, replica diode 122 and capacitor 123. The detector diode 121 and thecapacitor 123 form a negative peak detector. The detector diode 121 isbiased by current source 124, and the replica diode 122 is biased by amatching current source 125 so that the detector diode 121 and thereplica diode 122 track voltage drop over temperature and processvariations. In a representative embodiment, the diodes 121 and 122 havethe same areas, whence the current density in the diodes 121 and 122 isthe same. Other configurations of area and bias current that result inthe two diodes 121 and 122 having the same current density are thepresent teaching. Detection signal Det is output at the anode of thedetector diode 121 and reference signal Ref is output at the anode ofthe replica diode 122. The voltage of the reference signal Ref serves toinform the DC controller 130 what the critical voltage is for thedetection signal Det, at which point the output transistor 118 is deemedto be out of voltage and in need of a voltage boost. In other words, thereference signal Ref is the same as the detection signal Det that thedetector 120 would produce when the negative peaks of the collectorvoltage of the output transistor 118 reach the saturation voltage Vsat.The detection signal Det and the reference signal Ref are input to adetector encoder 430 of the DC controller 130, discussed below withreference to FIG. 4.

For purposes of illustration, the functionality of the detector 120 isimplemented using diodes: the detector diode 121 and the replica diode122. It should be apparent, however, that the detector diode 121 and thereplica diode 122 could be replace by transistors, respectively,functioning as diodes and therefore could be replaced with suchtransistors without change of functionality.

The detection signal Det represents an analog sample and hold process.It is the negative peak of the RF excursions of the collector of theoutput transistor 118, plus a forward voltage drop of the (diode wired)detector diode 121. The current source 124 provides a forward bias tothe detector diode 121. In an embodiment, the sizes of the detectordiode 121 and the replica diode 122 are the same, and the currents fromdetector current source 124 and the reference current source 125 are thesame. Then the forward voltage drop of the detector diode 121 and thereplica diode 122 at saturation of the power amplifier 110 areidentical, regardless of process and temperature variation. When thevoltage value of the detection signal Det descends down and interceptsthe voltage value of reference signal Ref, the DC controller 130instigates a boost operation, which supplies the output transistor 118with more operating voltage, as discussed below.

Increased operating voltage will shift the collector voltage waveform ofthe output transistor 118 up in voltage, hence the detection signal Detoutput by the (negative peak) detector 120 will rise. If the envelope ofthe RF output signal Vout drops in magnitude, the detection signal Detoutput by the detector 120 will rise further. When the envelope of theRF output signal Vout drops to a point where a recovery event could bedeployed without resulting in compression of the output transistor 118,the detection signal Det output by the detector 120 has risen to cross apredetermined threshold at which a recovery event is triggered. A boostevent is defined herein as a state change from a lower DC supply voltageto a sequentially adjacent higher DC supply voltage output by the DCcontroller 130. A recovery event is defined herein as a state changefrom a higher DC supply voltage to a sequentially adjacent lower DCsupply voltage output by the DC controller 130.

FIG. 4 is a block diagram illustrating the DC controller 130 of theamplifier circuit 100, according to a representative embodiment, asconnected to the detector 120, the power amplifier 110, and (a portionof) the compensation control circuit 200. Generally, the DC controller130 provides the DC supply voltage Vdc as the collector supply voltagefor the output transistor 118 of the power amplifier 110. The DCcontroller 130 also provides first and second compensating signals Comp1and Comp2 corresponding to the medium boost voltage Vmb and the highboost voltage Vhb, respectively, to the compensation control circuit200. In the depicted example, the compensation control circuit 200includes another feedback network that includes resistor 252, capacitor253, and compensation feedback switch 250, the state of which iscontrolled by the DC controller 130 via a second compensation signalComp2, discussed below.

Notably, the various circuits described herein may include a number ofseveral inverters, which are not depicted for the sake of clarity. Theinverters are used for the purpose of achieving desired switchingspeeds. As would be apparent to one of ordinary skill in the art, evennumbers of inverters in cascade make no logical contribution to circuitoperation, and the size and number of the inverters varies based onrequired speeds and currents from the DC controller 130, for example.

The collector supply voltage of the output transistor 118 is switchedamong three or more voltage values depending on the envelope of the RFinput signal Vin received at the signal input port 101 (not shown) andthe envelope of the respective RF output signal Vout. For purposes ofexplanation, an illustrative embodiment is described in which thecollector supply voltage is switched among three voltage values. Thefirst (smallest) voltage value is the boost voltage Vnb, which iseffectively the supply voltage (Vdd) with no voltage boost. The second(intermediate) voltage value and the third (largest) voltage valueprovide incrementally increasing boost voltage steps, obtained byboosting the supply voltage by different amounts. For example, thesecond voltage value is the medium boost voltage Vmb which may beapproximately one and a half times the supply voltage (1.5Vdd or1.5Vnb), and the third voltage value is the high boost voltage Vhb whichmay be approximately twice the supply voltage (2Vdd or 2Vnb).

For purposes of discussion, it is assumed that the amplifier circuit 100is included in a portable electronic device that is powered by abattery, and thus the supply voltage Vdd may be referred to as batteryvoltage Vbat. In this case, the no boost voltage Vnb may be the batteryvoltage Vbat (e.g., about 3.3V), which is equal to the battery voltageVbat provided by battery 111. The medium boost voltage Vmb may be1.5Vbat (e.g., about 4.95V), and the high boost voltage Vhb may be 2Vbat(e.g., about 6.6V). Stated differently, the medium boost voltage Vmb isequal to the no boost voltage Vnb (e.g., about 3.3V) plus a firstvoltage boost Vb1 (e.g., about 1.65V), and the high boost voltage Vhb isequal to the no boost voltage Vnb (e.g., about 3.3V) plus a secondvoltage boost Vb2 (e.g., about 3.3V). Accordingly, the collector supplyvoltage supports the maximum required power output only when that outputis specifically demanded. Otherwise, the collector supply voltage is themedium boost voltage Vmb or the battery voltage Vbat, again depending onthe instantaneous power level demanded, thus saving battery power of thebattery 111 as aggressively as possible at each point in time.

When no RF power is presented to the power amplifier 110, the DCcontroller 130 provides the no boost voltage Vnb as the DC supplyvoltage Vdc, and thus the collector supply voltage of the outputtransistor 118 is the same as the battery voltage Vbat. As the RF powerlevel increases, the collector supply voltage swings in both positiveand negative excursions in an operational envelope about the DC level.According to various embodiments, the envelope magnitude is effectivelyevaluated by the detector 120 in terms of the lowest occurring voltageextreme (negative peak voltage level or most negative RF excursion) atthe collector of the output transistor 118. The larger the RF powerlevel, the lower the lowest occurring voltage extreme will be.

When the lowest occurring voltage extreme stays above a predeterminedboost threshold (is within the predetermined boost threshold), thesupply voltage Vdc is unchanged. When the lowest occurring voltageextreme falls below a predetermined boost threshold (is beyond thepredetermined boost threshold), as indicated by the detector 120, the DCcontroller 130 switches to provide the medium boost voltage Vmb as thesupply voltage Vdc, which is roughly 1.5 times the previously availableno boost voltage Vnb to the collector, as discussed above. Similarly,when the lowest occurring voltage extreme again falls below thepredetermined boost threshold, as indicated by the detector 120, the DCcontroller 130 switches to provide the high boost voltage Vhb as thesupply voltage Vdc, which is roughly twice the no boost voltage Vnb tothe collector, as discussed above. The predetermined boost threshold maycorrespond to onset of the triode region of operation for the outputtransistor 118, at which point the power amplifier 110 no longeroperates properly (e.g., in saturation) and begins to compress severely.The voltage below which the power amplifier 110 no longer has goodamplifier characteristics may be referred to as the saturation voltageVsat.

After switching to the medium boost voltage Vmb, the DC controller 130maintains the medium boost voltage Vmb until the demand on the poweramplifier 110 is no longer sufficiently high, at which point the DCcontroller 130 switches back to the lower value no boost voltage Vnb, oruntil the demand progresses again to saturation, at which point the DCcontroller 130 switches to the high boost voltage Vhb. For example, whenthe lowest occurring voltage extreme exceeds a predetermined recoverythreshold (is beyond the predetermined recovery threshold), as indicatedby the detector 120, the DC controller 130 switches to again provide theno boost voltage Vnb as the supply voltage Vdc. After switching to thehigh boost voltage Vhb, the DC controller 130 maintains the high boostvoltage Vhb until the demand on the power amplifier 110 is no longerhigh. At this point, the DC controller 130 switches back to the lowervalue medium boost voltage Vmb or the no boost voltage Vnb, depending onthe extent of the demand and the relationship between the lowestoccurring voltage extreme and the predetermined recovery threshold.Switching from the no boost voltage Vnb to the medium boost voltage Vmb,and switching from the medium boost voltage Vmb to the high boostvoltage Vhb, may be referred to as boost events. Switching from the highboost voltage Vhb to the medium boost voltage Vmb, and switching fromthe medium boost voltage Vmb to the no boost voltage Vnb, may bereferred to as recovery events.

In order to avoid unwanted distortion, complex gain of the poweramplifier 110 may be compensated when the collector supply voltage isincreased to the medium boost voltage Vmb or the high boost voltage Vhb.For example, it is possible for performance parameters of the outputtransistor 118 of the power amplifier 110 to change in response tochanges in supply voltage enforced by the DC controller 130. This cangive rise to unwanted non-linear artifacts that degrade modulationintegrity and adjacent channel leakage performance. The complex gaincompensation may be performed by the compensation control circuit 200.

Referring to FIG. 4, the DC controller 130 includes power switch 410,switch sequencer 420 and detector encoder 430. Generally, the detectorencoder 430 receives the analog detection signal Det and the analogreference signal Ref output from the detector 120, which indicate whenthe output signal Vout of the output transistor 118 of the poweramplifier 110 has reached the predetermined boost threshold (e.g.,saturation). The detector encoder 430 translates the detection signalDet and the reference signal Ref into a two bit word, where the firstbit provides a Boost Request signal and the second bit provides aRecovery Request signal. The switch sequencer 420 receives the BoostRequest signal and the Recovery Request signal, enabling it to translatethe detection signal Det and the reference signal Ref into a five bitword, including first through fifth control bits Vc1 to Vc5. The firstthrough fifth control bits Vc1 to Vc5 are provided to the power switch410. In response, the power switch 410 coordinates switching among theno boost voltage Vnb (e.g., supply voltage Vdd), the medium boostvoltage Vmb and the high boost voltages Vhb, and outputs the selectedvoltage as the DC supply voltage Vdc to the power amplifier 110. Thatis, the power switch 410 operates under control of the first throughfifth control bits Vc1 to Vc5 to pass through the supply voltage Vdd (ina pass-through state) or to boost on demand the battery voltage Vbat toone of the medium boost voltage Vmb or the high boost voltage Vhb, asdiscussed below.

Thus, when the output of the detector 120 falls to the critical voltageat which the collector supply for the power amplifier 110 must beboosted to the medium boost voltage Vmb (1.5Vbat), the detector encoder430 generates a Boost Request signal (indicated by a rise of the BoostRequest bit from a 0 to a 1) for the switch sequencer 420. Once the DCcontroller 130 has complied with the boost request the Boost Request bitof the detector encoder 430 returns to 0. After this operation, if theoutput of the detector 120 falls to the critical voltage again at whichthe collector supply for the power amplifier 110 must be boosted to thehigh boost voltage Vhb (2Vbat), the detector encoder 430 generates aboost request again. However, if the output of the detector 120 rises tothe critical voltage at which the collector supply for the poweramplifier 110 does not need the medium boost voltage Vmb or the highboost voltage Vhb anymore, then the detector encoder 430 generates aRecovery Request signal (indicated by a rise of the Recovery Request bitfrom a 0 to a 1) for the switch sequencer 420. Once the DC controller130 has complied with the recovery request, the Recovery Request bit ofthe detector encoder 430 returns to 0.

In an embodiment, the DC supply voltage Vdc is also fed back to thedetector encoder 430 as a bias voltage. Generally, when a recovery eventis indicated by the appropriate conditions of relaxed carrier envelopemagnitude, the output voltage of the detector 120 is relatively high. Inorder to maintain proper bias current through the detector diode 121,the corresponding current source 124 (FIG. 3) must have sufficientvoltage compliance to maintain this current at the higher output voltageof the detector 120. To achieve this end, the current source 124 must bepowered by a higher voltage than the battery voltage Vbat, hence it isconvenient to power the current source 124 circuit with the DC supplyvoltage Vdc of the DC controller 130. For example, the output voltage ofthe detector 120 is high only when there is currently a boosted state,at which times the DC supply voltage Vdc is sufficiently high to keepthe current source 124 circuit properly biased. In order to maintainabsolute symmetry between the detector diode 121 and the replica diode122, the DC supply voltage Vdc is also used to bias the referencecurrent source 125.

In addition, the DC controller 130 includes fault recovery circuit 440for detecting faults in the DC supply voltage Vdc, provided as a samplevoltage by the power switch 410. Herein, a fault refers to aninsufficiency in the boosted DC supply voltage Vdc as a result ofexcessive discharge of first charge storage capacitor 811 and/or secondcharge storage capacitor 812 of the power switch 410 (as shown in FIG.8). Based on the fault detection, the fault recovery circuit 440 outputsan Enable signal to the switch sequencer 420 to selectively enableoperation of the switch sequencer 420, discussed below with reference toFIGS. 13A to 13C. The fault recovery circuit 440 thus disables the boostvoltage in case of a fault in both medium boost state MB and high booststate HB, for a time period which is sufficient to permit the firstcharge storage capacitor 811 and the second charge storage capacitor 812of power switch 410 to fully recharge. The DC controller 130 alsoincludes charge pump voltage source 450 for generating a charge pumpvoltage Vqp, which is approximately 1.5 to 2 times the battery voltageVbat, discussed below with reference to FIG. 22.

FIG. 5 is a circuit diagram of a detector bias circuit 500, togetherwith the power amplifier stage, indicated by output transistor 118 andinductor 115, and the detector 120, according to a representativeembodiment. In the depicted embodiment, the detector bias circuit 500 isincluded within the detector encoder 430, as shown in FIG. 6, forexample, although the detector bias circuit 500 may be configuredseparately or within another component without departing from the scopeof the present teachings.

Referring to FIG. 5, the detector bias circuit 500 includes twoidentical detector bias current sources 501 and 502, which bias thedetector diode 121 and the reference diode 122 of the detector 120,respectively. The detector bias current sources 501 and 502 are poweredfrom the DC supply voltage Vdc output by the DC controller 130, enablingthe detector bias current sources 501 and 502 to comply with the higheroutput voltage of the detector 120 when voltage boost is present. Thatis, the DC supply voltage Vdc supplies the detector bias current sources501 and 502 with sufficient operating voltage to comply with the outputof the detector 120 when boost is present.

During negative peaks of the output transistor 118, collector voltage atthe detector diode 121 is forward biased, and the anode of the detectordiode 121 follows the cathode. The cathode voltage is then stored in thecapacitor 123. During more positive values of the collector voltage, theoutput voltage (detection signal Det) remains stored across thecapacitor 123, hence detector diode becomes reverse biased and cannotdischarge the capacitor 123. The capacitor 123 may be referred to as avideo filter capacitor. The Det and Ref lines are coupled directly tothe input ports of the boost comparator 610, as discussed below withreference to FIG. 6. When the negative peaks of the collector voltage ofthe output transistor 118 intercept the saturation voltage Vsat, theresult is that the detection signal Det is equal to the reference signalRef and the boost comparator 610 will switch states to initiate a boostevent. Two additional output ports 515 and 525, for outputting scaleddetection signal Det2 and scaled and offset reference signal Ref2, areprovided as inputs to the recovery comparator 620, also as discussedbelow with reference to FIG. 6.

Recovery occurs when the output voltage of the DC controller 130 isboosted and the output power of the output transistor 118 issufficiently low that boost is no longer needed (the lowest occurringvoltage extreme is above the predetermined recovery threshold). In thiscase the output of the detector 120 is relatively high. To keep thevoltages of the scaled detection signal Det2 and the scaled and offsetreference signal Ref2 low enough to be in the operating range of therecovery comparator 620, the scaled detection signal Det2 is created bydividing detection signal Det down by the divider ratio determined bythe values of resistors 512 and 513. The scaled and offset referencesignal Ref2 is created by dividing the reference signal Ref down for thesame reason by the values of resistors 522 and 523, and then adding aspecific offset voltage Voffset dropped across resistor 524. It can beshown that the offset voltage is advantageously derived as a fraction ofthe battery voltage Vbat. The situation may be summarized by theEquations (1) and (2):Det2=α*Det  (1)Ref2=(α*Ref)+Voffset  (2)

The value α is the voltage divider ratio produced by resistors 512 and513, and again by resistors 522 and 523. As previously stated, it is avalue less than unity that keeps the inputs to the recovery comparator620 within its operating range. The remaining circuitry of the detectorbias circuit 500 includes a voltage divider, formed by resistors 531 and532, to fractionate the battery voltage Vbat. Operational amplifier 534biases PMOS transistors 541, 542 and 543 to achieve the samefractionated supply voltage at the non-inverting input of theoperational amplifier 534. The current thus produced in resistor 535connected to the non-inverting input of the operational amplifier 534 ismirrored by the circuit comprising resistor 536 and mirror PMOStransistors 551 and 552, so that this current, or a known scaled versionof this current, is forced through the resistor 524.

A boost event is instigated when the negative peaks of the collectorvoltage of output transistor 118 reach the value of saturation voltageVsat, a predetermined value at which the output transistor 118 begins tosaturate. Representing the detector diode 121 forward voltage drop asVf, the detector output voltages immediately before a boost event may bewritten as Equations (3) and (4):Det=Vsat+Vf  (3)Ref=Vsat+Vf  (4)

Immediately after the boost event, the detection and reference signalsare provided by Equation (5):Det=Vsat+Vf+0.5Vbat  (5)

Assuming that an infinitesimal reduction in RF power from the poweramplifier 110 would allow the boost to be forfeited, recovery isexpected immediately after the boost occurs, in which case the scaleddetection and reference signals Det2 and Ref2 are provided by Equations(6) and (7):Det2=alpha*(Vsat+Vf+0.5Vbat)  (6)Ref2=alpha*(Vsat+Vf)+Voffset  (7)

A recovery event is instigated when Det2=Ref2, from which the offsetvoltage Voffset may be solved according to Equation (8):Voffset=α*0.5Vbat  (8)

If α were chosen to be 0.5, for example, then the offset voltage Voffsetwould be 0.25Vbat. The battery voltage Vbat is typically 3.4V in a cellphone application, for example, hence Voffset=850 mV.

The situation described above may lead to system instability because aboost event would immediately trigger a recovery event. Thus, tostabilize the system, a small amount of hysteresis is needed. Thishysteresis comes from the power amplifier 110 because, for efficiencypurposes, the power amplifier 110 enters slightly into compressionbefore the boost event is triggered. In this case the response of thenegative peak detector 120 is slightly less than would be expected,e.g., it is slightly less than 0.5Vbat. Additionally, the actual voltagestep produced by the DC controller 130 is less than 0.5Vbat due tolosses in the power switch 410. The result is typically an excessiveamount of hysteresis, with concomitant reduced efficiency. Thehysteresis can be dropped to a more desirable value by reducing theoffset voltage Voffset by a few hundred mV, for example.

The detection signal Det, the reference signal Ref, the scaled detectionsignal Det2, and the scaled reference signal Ref2 are then fed into theboost comparator and the recovery comparator, as shown in FIG. 6.

FIG. 6 is a block diagram illustrating a detector encoder 430 of the DCcontroller 130, according to a representative embodiment. Generally, thedetector encoder 430 of the DC controller 130 encodes the detection andreference signals into a two bit digital word. Functions of detectorencoder 430 include providing bias currents to the detector diode 121and the reference diode 122, comparing the detection signal Det with thereference signal Ref, and comparing the scaled detection signal Det2 tothe scaled and offset reference signal Ref2 to produce the Boost andRecovery Request signals, respectively.

Referring to FIG. 6, the Boost and Recovery Request signals provideinput states for the switch sequencer 420 based on the analog detectionsignal Det and the analog reference signal Ref. In various embodiments,the detector encoder 430 includes the boost comparator 610 and therecovery comparator 620, mentioned above. The boost and recoverycomparators 610 and 620 may be implemented as operational amplifiers,for example. The boost comparator 610 includes a positive(non-inverting) input that receives the detection signal Det from thedetector 120, and a negative (inverting) input that receives referencesignal Ref from the reference detector 120. The boost comparator 610compares the detection signal Det and the reference signal Ref, and thecomparison result is inverted by inverter 640 to output the BoostRequest signal. The recovery comparator 620 includes a positive inputthat receives the scaled detection signal Det2 from the detector biascircuit 500, and a negative input that receives the scaled and offsetreference signal Ref2 from the detector bias circuit 500. The recoverycomparator 620 compares the scaled detection signal Det2 and the scaledreference signal Ref2, and outputs the Recovery Request signal as thecomparison result.

In operation, when the detection signal Det falls below the referencesignal Ref, e.g., which happens when the negative peak on the collectorof the power amplifier 110 falls below the saturation voltage Vsat, theBoost Request signal output by the inverter 611 has a rising edge.Likewise, when the scaled detection signal Det2 rises above the scaledand offset reference signal Ref2, the Recovery signal output by therecovery comparator 620 has a rising edge, signaling a recovery request.Notably, a recovery event will not be triggered unless the magnitude ofthe envelope of the RF output signal Vout has fallen to a point where arecovery event will not result in compression. The value of the outputvoltage Vout at which recovery occurs, as determined by the value ofRef2, is important in that too low a value of Vout would result inwasted opportunity to reduce operating voltage, with resultant loss ofefficiency.

A boost event results in a rise in the output of the detector 120 thatis approximately equal to one voltage step of the DC controller 130. Ina three-state system, for example, the voltage step may be about0.5Vbat. Before a recovery event is permitted, some drop in envelopemagnitude of the RF input signal Vin must occur so that the recoveryevent does not result in compression. Unless this drop is required forrecovery, the system will become unstable (oscillate between boost andrecovery). The required envelope magnitude drop must be small, so thatrecovery can be triggered as soon as it is possible. Late recovery wouldreduce efficiency. In the three-state system, for example, the negativepeak voltage Vngpk at which recovery is possible is given by Equation(9), where Vhys is a small hysteresis margin voltage sufficient to keepthe system stable:Vngpk˜Vsat+0.5Vbat+Vhys  (9)

Under the condition of Equation (9), the detection signal Det may beprovided by Equation (10), where Vf is the forward voltage drop of thedetector diode 121:Det=Vsat+Vf+0.5Vbat+Vhys  (10)

Since the operating voltage step 0.5Vbat is much larger than hysteresismargin voltage Vhys (0.5Vbat>>Vhys), it is appropriate to create theoffset voltage Voffset as a fractional representation of the batteryvoltage Vbat. By doing this, the solution is insensitive to the specificvalue of the battery voltage Vbat. The hysteresis margin voltage Vhys issmall and can be determined by experimentation, for example. When thesaturation voltage Vsat is set sufficiently low that a boost event isnot triggered until a small amount of compression occurs in the poweramplifier 110, then it is possible to operate with the hysteresisvoltage Vhys less than or equal to 0V. This is because the compressedpower amplifier 110 will produce a rise in the collector negative peakvoltage that is somewhat smaller than the size of the operating voltagestep (e.g., 0.5Vbat), and this reduced rise is sufficient to maintainstability of the system.

FIG. 7 is a circuit diagram illustrating the switch sequencer 420 of theDC controller 130, according to a representative embodiment.

Referring to FIG. 7, the switch sequencer 420 generally translates theBoost Request signal and the Recovery Request signal, output by thedetector encoder 430 and received at port BR and port RR, respectively,into multiple control signals for controlling operations of the powerswitch 410. The switch sequencer 420 also receives the DC supply voltageVdc output by the power switch 410 (which is also output by the DCcontroller 130) at input port In1, mid-capacitor voltage Vmcap output bythe power switch 410 at input port In2, and Enable signal output by thefault recovery circuit 440 at port Enable. In the depicted embodiment,the control signals include first control bit Vc1, second control bitVc2, third control bit Vc3, fourth control bit Vc4, and fifth controlbit Vc5, which are provided to the power switch 410. The switchsequencer 420 also outputs first and second compensation control signalsComp1 and Comp2 to the compensation the control circuit 200.Additionally, the switch sequencer 420 outputs the Gate2 and Gate3signals to the fault recovery circuit 440. Generally, the purpose of theswitch sequencer 420 is to operate the power switch 410 into apass-through state and multiple boost states, as needed. The switchsequencer 420 is discussed in detail, below, following discussion of thepower switch 410.

FIG. 8 is a circuit diagram illustrating the power switch 410 of the DCcontroller 130, according to a representative embodiment.

Referring to FIG. 8, the power switch 410 receives the first throughfifth control bits Vc1 to Vc5 from the switch sequencer 420, and outputsthe supply voltage Vdc to the power amplifier 110 in one of three modes,in accordance with the first through fifth control bits Vc1 to Vc5. Thepower switch 410 also outputs mid-capacitor voltage Vmcap at the commonnode connection (fourth node 824) between the first and second chargestorage capacitors 811 and 812, which enables monitoring of chargesymmetry between the first and second charge storage capacitors 811 and812.

The power switch 410 includes first transistor 801A, second transistor801B, third transistor 801C, fourth transistor 802, fifth transistor803, sixth transistor 804 and seventh transistor 805, which arecontrolled by the first through fifth control bits Vc1 to Vc5,respectively. More particularly, in the depicted embodiment, the firsttransistor 801A is an NMOS FET that includes a gate controlled by thefirst control bit Vc1, a source connected to the battery voltage Vbat,and a drain connected to first node 821 (output node for DC supplyvoltage Vdc) located at the output for providing the DC supply voltageVdc. The second transistor 801B is an NMOS FET that includes a gatecontrolled by the first control bit Vc1, a source connected to secondnode 822 located between the second capacitor 612 and the fourthtransistor 802. The third transistor 801C is an NMOS FET that includes agate controlled by the first control bit Vc1, a source connected toground, and a drain connected to third node 823 located between thesixth transistor 804 and the first charge storage capacitor 811. Thefourth transistor 802 is a PMOS FET that includes a gate controlled bythe second control bit Vc2, a source connected the second node 822, anda drain connected to the first node 821. The fifth transistor 803 is aPMOS FET that includes a gate controlled by the third control bit Vc3, asource connected to the first node 821, and a drain connected to afourth node 824 (output node for mid-capacitor voltage Vmcap) locatedbetween the first and second charge storage capacitors 811 and 812. Thesixth transistor 804 is a PMOS FET that includes a gate controlled bythe fourth control bit Vc4, a source connected to the battery voltageVbat, and a drain connected to the third node 823. The seventhtransistor 805 is an NMOS FET that includes a gate controlled by thefifth control bit Vc5, a source connected to the fourth node 824, and adrain connected to the battery voltage Vbat.

In the depicted embodiment, the first, second, third and seventhtransistors 801A, 801B, 801C and 805 are NMOS FETs, and the fourth,fifth and sixth transistors 802, 803 and 804 are PMOS FETs. However,other types of FETs and/or other types of transistors may beincorporated without departing from the scope of the present teachings.Further, for clarity, body contacts of the various NMOS and PMOS FETsthroughout the figures and specification have not been shown withrespect to where and how they may be connected/biased. However, suchconfigurations would be apparent to one of ordinary skill in the art.

In the depicted embodiment, the power switch 410 has four states: state1, state 2A, state 2B, and state 3. State 1, defined as the Vbatpass-through state, is achieved by turning on the first transistor 801A,the second transistor 801B, the third transistor 801C and the fourthtransistor 802, and turning off the other transistors. In state 1, thebattery voltage Vbat is passed through the first transistor 801A to thefirst node 821 to be output as the DC supply voltage Vdc, which isprovided to the output transistor 118 of the power amplifier 110. Alsoin state 1, the first and second charge storage capacitors 811 and 812are connected between the battery voltage Vbat and ground though thesecond transistor 801B and the third transistor 801C, which allows themto collectively charge up to the battery voltage Vbat. That is, each ofthe first and second charge storage capacitors 811 and 812 charge to acapacitor voltage value of about 0.5Vbat. The first and second chargestorage capacitors 811 and 812 normally have the same capacitance value,so that one can consider same voltage and same charge interchangeably.

State 2A, defined as the first of two boost states producing 1.5Vbat, isachieved by turning on the fifth transistor 803 and the sixth transistor804, and turning of the other transistors. In state 2A, the top of thefirst charge storage capacitor 811 is connected to the first node 821via the fifth transistor 803, and the bottom of the first charge storagecapacitor 811 is connected to the battery voltage Vbat via the sixthtransistor 804. The voltage across the first charge storage capacitor811 is Vbat/2, hence the load at the first node 821 sees approximately1.5Vbat. State 2B, defined as the second of two boost states producing1.5Vbat, is achieved by turning on the fourth transistor 802 and theseventh transistor 805, and turning off the other transistors. In state2B, the top of the second charge storage capacitor 812 is connected tothe first node 821 via the fourth transistor 802, and the bottom of thesecond charge storage capacitor 812 is connected to the battery voltageVbat via the seventh transistor 805. The voltage across the secondcharge storage capacitor 812 is Vbat/2, hence the load at the first node821 sees approximately 1.5Vbat.

State 3, defined as the boost state producing 2Vbat, is achieved byturning on the fourth transistor 802 and the sixth transistor 804, andturning off the other transistors. In state 3, the top of the secondcharge storage capacitor 812 is connected to the first node 821 via thefourth transistor 802, and the bottom of the first charge storagecapacitor 811 is connected to the battery voltage Vbat via the sixthtransistor 804. The voltage across the series combination of the firstand second charge storage capacitors 811 and 812 is Vbat, hence the loadat the first node 821 sees approximately 2Vbat.

The type of FET, i.e. NMOS or PMOS, for each of the first throughseventh transistors 801A to 805 is chosen in each case depending on thevoltages that are being switched, in such a way that the resultant gatedrive voltage is between 0V and 2Vbat, and the required magnitude ofvoltage step at each gate to switch each of the first through seventhtransistors 801A to 805 between on and off states is Vbat. Under thisconstraint, all gates may be driven from Vbat biased logic having stateswing of Vbat and level shifted by approximately Vbat, as necessary.Further, as mentioned above, the first, second, third and seventhtransistors 801A, 801B, 801C and 805 are chosen to be NMOS FETs, and thefourth, fifth and sixth transistors 802, 803 and 804 are chosen to bePMOS FETs. Also, the first, second, fourth, fifth and seventhtransistors 801A, 801B, 802, 803 and 805 each require level shifting,while the third and sixth transistors 801C and 804 are driven directlyfrom battery voltage Vbat biased logic. This situation is described inthe Table 1, which shows (approximated) gate voltages (Vg) of thetransistors, for purposes of illustration.

TABLE 1 State Vg801A Vg801B Vg801C Vg802 Vg803 Vg804 Vg805 NMOS NMOSNMOS PMOS PMOS PMOS NMOS on 2Vbat 2Vbat Vbat Vbat Vbat 0 2Vbat off VbatVbat 0 2Vbat 2Vbat Vbat Vbat

The states are summarized in the Table 2 as follows:

TABLE 2 801A 801B 801C 802 803 804 805 State on on on on off off off 1off off off off on on off 2A off off off on off off on 2B off off off onoff on off 3

From Table 2, it can be seen that the first, second and thirdtransistors 801A, 801B and 801C switch together. In other words, theyare either all on or all off Therefore, the first, second and thirdtransistors 801A, 801B and 801C may be driven by a single control line(in this example, Vc1), and thus the power switch 410 may be controlledby a five bit parallel bus. Of course, the transistors may be driven byseparate control signals in various embodiments, without departing fromthe scope of the present teachings.

Accordingly, the third transistor 801C is driven directly by the firstcontrol bit Vc1 from a corresponding bus line, and the sixth transistor804 is driven directly by the fourth control bit Vc4 from acorresponding bus line. The first and second transistors 801A and 801Bare driven by the first control bit Vc1 after level shifting, indicatedin FIG. 8 as Vc1 _(LS). The fourth transistor 802 is driven by thesecond control bit Vc2 from a corresponding bus line after levelshifting, indicated as Vc2 _(LS). The fifth transistor 803 is driven bythe third control bit Vc3 from a corresponding bus line after levelshifting, indicated as Vc3 _(LS). The seventh transistor 805 is drivenby the fifth control bit Vc5 from a corresponding bus line after levelshifting, indicated as Vc5 _(LS).

FIG. 8 depicts level shifters 410 a and 410 b corresponding to the levelshifting requirements of the control bit bus lines discussed above. Eachof the first control bit Vc1 and the third control bit Vc3 are levelshifted by a corresponding level shifter 410 a, although only the levelshifter 410 a used for level shifting the first control bit Vc1 isdepicted and discussed for the sake of convenience. Likewise, each ofthe second control bit Vc2 and the fifth control bit Vc5 are levelshifted by a corresponding level shifter 410 b, although only the levelshifter 410 b used for level shifting the second control bit Vc2 isdepicted and discussed for the sake of convenience. It is understoodthat the level shifters 410 a and 410 b function in substantially thesame manner described below for the third control bit Vc3 and the fifthcontrol bit Vc5, respectively, to provide the level shifted thirdcontrol bit Vc3 _(LS) and the level shifted fifth control bit Vc5 _(LS).The fourth control bit Vc4 does not require a level shifter.

The level shifter 410 b is a simple diode RC level shifter. The levelshifter 410 b includes capacitor 841 connected between an input toreceive the second control bit Vc2 and an output to provide the levelshifted second control bit Vc2 _(LS). Diode 842 is connected between thebattery voltage Vbat and the output, and resistor 843 is connectedbetween the output and ground. Thus, the level shifter 410 b operates bycharging up the capacitor 841 through the diode 842 when the secondcontrol bit Vc2 is in the low state. When second control bit Vc2 is inthe high state, the voltage across the capacitor 841 is added to the busvoltage to produce an offset of about Vbat−Vf, where Vf is the forwardvoltage drop across the diode 842. The resistor 843 ensures that thelevel shift does not float to some higher value than Vbat−Vf. Hereafterthe magnitude of level shift will be referred to simply as Vbat. Properoperation of the level shifter 410 b requires that the capacitor 841stays charged, and due to various leakage currents that are inevitable,this requires continual assertion of logic low on the corresponding buslines.

The level shifter 401 a is a more sophisticated circuit. The reason forthis is found by observing that the power switch 410 may remain in state1 for an extended period of time, such as would happen if the powerrequirement from the power amplifier 110 were very low. In this case,the first transistor 801A and the second transistor 801B must remain on,requiring a level shifted logic high. Also, the fifth transistor 803must remain off, and also requiring a level shifted logic high. Withoutthe additional level shifter circuitry depicted in the level shifter 410a, capacitor 834 may eventually discharge causing the level shiftvoltage to collapse.

To prevent this, inverter 836 produces a logic low, which is levelshifted by a level shifter comprised of capacitor 831, diode 832 andresistor 833. This level shifted logic low is then fed to the gate oftransistor 838, which is a PMOS FET, the source of which is biased by acharge pump voltage Vqp which is approximately 2Vbat. Thus thetransistor 838 is held in the on state whence the charge pump voltageVqp is coupled to the output of the level shifter 410 a through resistor837. The resistor 837 then supplies whatever leakage current is demandedby the capacitor 834, including its own leakage current, so that thecapacitor 834 is prevented from discharging. If the capacitor 831 wereto discharge, the transistor 838 would remain on, so that the levelshifted first control bit Vc1, i.e. Vc1 _(LS), remains level shiftedindefinitely. When the first control bit Vc1 goes low, the gate of thetransistor 838 goes high, e.g. to approximately 2Vbat, which turns offthe transistor 838 and allows the level shifted first control bit Vc1_(LS) to achieve a logic low. One need not consider the case where thefirst control bit Vc1 is held in the low state indefinitely, thuscausing an eventual collapse in the level shifted logic high appearingat the gate of the transistor 838 because the DC controller 130 cannotremain in a boosted state indefinitely.

The drive bus states and the corresponding states of the power switch410 are summarized in the Table 3 below:

TABLE 3 Vc1 Vc2 Vc3 Vc4 Vc5 state 1 0 1 1 0 1 0 1 0 0 0 2A 0 0 1 1 1 2B0 0 1 0 0 3

It is the task of the switch sequencer 420 to produce these four 5-bitwords (states 1, 2A, 2B, 3) in accordance with the voltage needed by thepower amplifier 110 at each point in time.

Referring again to FIG. 7, the switch sequencer 420 is configured todrive the power switch 410 into each of the various modes or states(e.g., four states for providing three voltage levels in the depictedembodiment) and to transition between the states with the correctsequence so that no shoot-through current occurs in the power switch410. More specifically, the switch sequencer 420 sequences thetransitions among states, for example, so that at no time are first andsecond charge storage capacitors 811 and 812 (depicted in FIG. 8)shorted by the power switch 410. If shoot-through current were to occur,it would negatively impact efficiency. The switch sequencer 420 is ableto generate the first through fifth control bits Vc1 to Vc5 as controlsignals to drive the power switch 410 in the various states. In thedepicted embodiment, the switch sequencer 420 include various encoders,including clock encoder 710, x-encoder 720, S1 clock encoder 730,abc-encoder 740, w-encoder 750, driver decoder 760 and compensationdecoder 770, each of which are described below. Generally, operation ofthe switch sequencer 420 begins with the Boost Request signal and theRecovery Request signal received at the ports BR and RR, respectively,from the detector encoder 430. When the power amplifier 110 requiresboost, the detector encoder 430 asserts a rising edge from the BoostRequest signal to trigger a boost event. When boost is no longer needed,the detector encoder 430 asserts a rising edge from the Recovery Requestsignal to trigger a recovery event. The DC supply voltage Vdc output bythe DC controller 130 is provided as an input to the input port In1 ofthe switch sequencer 420 as a means of indicting the present state ofthe DC controller 130 at the time the event request is made by the poweramplifier 110. With these three pieces of information the DC controller130 can take the appropriate action, as shown in Table 4 below:

TABLE 4 Current State Event Requested Required Action State 1 RecoveryNone State 1 Boost Switch to State 2 State 2 Recovery Switch to State 1State 2 Boost Switch to State 3 State 3 Recovery Switch to State 2 State3 Boost None

In addition to these tasks, the DC controller 130 is able to evaluatethe charge on the charge storage capacitors 811 and 812 of the powerswitch 410, and to take the appropriate action to maintain sufficiencyand symmetry of the charge. Sufficiency is typically not a problem undernormal operation, but in case of excessive input power to the poweramplifier 110 and the resultant low occupancy of state 1, the charges ofthe charge storage capacitors 811 and 812 may become depleted. If thishappens during either state 2 or state 3, the charges can be restored byreverting to and sustaining state 1 for a predetermined period of time.Detecting and initiating restoration for such a discharge problem isperformed by the fault recovery circuit 440, discussed below. The switchsequencer 420 includes the facilities that permit execution of thecharge recovery task.

In accordance with the fault recovery mentioned above, the DC supplyvoltage Vdc output by the DC controller 130 is sampled to determine theadequacy of charge as revealed by the DC supply voltage Vdc in state 2and state 3. This sampling is performed through input port In of thefault recovery circuit 440, in accordance with FIG. 4, discussed above.

Also, as mentioned above, mid-capacitor voltage Vmcap is output by thepower switch 410 at the fourth node 824, located between the first andsecond charge storage capacitors 811 and 812. The mid-capacitor voltageVmcap is fed back to the switch sequencer 420 via the input port In2 toenable monitoring of the charge symmetry between the first and secondcharge storage capacitors 811 and 812 and triggering appropriate actionto maintain symmetry. More specifically, a charge manager circuit in thedriver decoder 760, discussed below, compares the charges of the firstand second charge storage capacitors 811 and 812 of the power switchduring state 1. The next time state 2 is needed, the charge managercircuit directs the power switch to use the one of the first and secondcharge storage capacitors 811 and 812 with the most charge, thuscontinually steering the charge toward symmetry between the first andsecond charge storage capacitors 811 and 812.

FIG. 9A is a logic circuit diagram of the clock encoder 710 of theswitch sequencer 420, according to a representative embodiment. Theclock encoder receives the Boost Request signal at port BR and theRecovery Request signal at port RR. The clock encoder 710 includesinverter 711 that inverts the Recovery Request signal, NAND gate 712that performs a NAND operation on the Boost Request signal and theRecovery Request signal, and exclusive NOR gate 713 that performs anexclusive NOR operation on the output of the NAND gate 712 and theRecovery Request signal. The output of the NAND gate 712 is provided toBRx output as BRx signal, and the output of the exclusive NOR gate 713is provided to clk output as clk signal.

The purpose of the clock encoder 710 is to produce a rising edge on theclk output in response to a request by the power amplifier 110 for anevent, whether a boost event or a recovery event. The BRx output is usedto identify the request as corresponding to a boost event or a recoveryevent. Table 5 provides a truth table reflecting the illustrativeconfiguration of the clock encoder 710.

TABLE 5 BR RR BRx clk Description 0 0 1 0 Amplifier Satisfied 1 0 0 1Boost Request 0 1 1 1 Recovery Request 1 1 1 1 N/A

Table 5 shows that the clk signal transitions from 0 to 1 when an eventis requested. The BRx signal is 0 or 1 depending on whether the requestis for a boost event or a recovery event, respectively.

FIG. 9B is a circuit diagram showing inverter 711 of the clock encoder710, according to a representative embodiment. The inverter 711 is ofthe slow rise variety, and includes first transistor 714, secondtransistor 715, resistor 716 connected between the source of the firsttransistor 714 and the drain of the second transistor 715, and capacitor717 connected to the drain of the second transistor 715. The firsttransistor 714 is a PMOS FET and the second transistor 715 is an NMOSFET, both of which are gated by the Recovery Request signal. It isevident from FIG. 9A that the clock encoder 710 cannot respond to aBoost Request signal until the preceding Recovery Request signal hasabated, and the output of the inverter 711 has risen to a value of 1.The slow rise characteristic of the inverter 711 ensures that therecovery has settled before allowing a Boost Request signal to beclocked, thus enhancing the stability of the system.

FIG. 10 is a circuit diagram of the x-encoder 720 of the switchsequencer 420, according to a representative embodiment. Generally, itis not sufficient simply to know whether a boost event or a recoveryevent is requested by the power amplifier 110. The current state of theDC controller 130 must also be known before the specific action inresponse to the requested boost event or recovery event can bedetermined. The x-encoder 720 is used to discern the current outputstate of the DC controller 130 at the time the event request is made bythe power amplifier.

Referring to FIG. 10, the x-encoder 720 includes first and secondcomparators 721 and 722, each receiving a fractionated sampling voltagev1 of the DC supply voltage Vdc output by the DC controller 130 by wayof the input port In1. The fractionated sampling v1 is coupled to thenon-inverting input of each of the first comparator 721 and the secondcomparator 722. Resistor 723 is connected between the non-invertinginput of the first comparator 721 and the input port In1, and resistor724 is connected between the non-inverting input of the secondcomparator 722 and ground. A resistive voltage divider providesreference voltages v2 and v3 to the inverting inputs of the firstcomparator 721 and the second comparator 722, respectively. The voltagedivider includes resistors 725, 726 and 727 connected between the powersupply port Vbat and ground, where the reference voltage v2 is thevoltage between resistors 725 and 726 and the reference voltage v3 isthe voltage between resistors 726 and 727.

From FIG. 10, it can be seen that v3<v2. If v1<v3 then the DC controller130 is deemed to be in state 1 and the outputs x0 and x1 are both 0. Thevalues of resistors 723 and 724 are chosen so that the fractionatedsampling v1 is always within the operating range of the first and secondcomparators 721 and 722. Resistors 725, 726 and 727 are chosen so thatthe following statements are true:

-   -   v1<v3, state 1 of DC controller 130    -   v3<v1<v2, state 2 of DC controller 130    -   v1>v2, state 3 of DC Controller 130

Thus the circuit's behavior is summarized in Table 6 below:

TABLE 6 DC Controller State x0 x1 state 1 0 0 state 2 1 0 state 3 1 1

Capacitors 771-774 provide displacement current needed by the inputs ofthe first comparator 721 and the second comparator 722 during rapidslewing of the DC supply voltage Vdc. Capacitor 771 is connected inparallel with resistor 723. Capacitor 772 is connected in parallel withresistor 724. Capacitor 774 is connected in parallel with resistor 727.Capacitor 773 is connected in parallel with the circuit containingcapacitor 774 and resistors 726 and 727. More particularly, the ratio ofvalues of 1/capacitor 771 to 1/capacitor 772 is preferably equal to theratio of values of resistor 723 to resistor 724. This ensures that thex-encoder 720 settles quickly after a state change of the DC controller130. In an alternate embodiment, the switch sequencer 420 does notinclude the x-encoder 720, and the x0 and x1 bits are taken directlyfrom the Comp1 and Comp2 bits, respectively.

FIG. 11A is a circuit diagram of the abc-encoder 740 of the switchsequencer 420, according to a representative embodiment. FIG. 11B is alogic circuit diagram of an SR-latch in the abc-encoder, according to arepresentative embodiment.

Generally, the purpose of the abc-encoder 740 is to combine the eventrequests of the power amplifier 110 together with the current state ofthe DC controller 130 at the time of the requests, and to generateresponse codes in the form of output signals a, b and c that willinstruct the power switch 410 to take the appropriate action. Theabc-encoder 740 includes latches 741 and 742 for latching the values ofthe inputs x0 and x1 (provided by the x-encoder 720) to outputs a and b,respectively, to provide output signals a and b when the clock signalclk has a rising edge. Based on the foregoing explanations, it can bestated that the inputs x0 and x1 together represent the instantaneousoutput voltage state of the DC controller 130 at the time that an eventrequest is asserted, and those values of the inputs x0 and x1 arelatched to outputs a and b, respectively. The abc-encoder 740 performsanother independent operation using SR-latch 743, which latches the BRxsignal and the Recovery Request signal to output c to provide outputsignal c. Capacitor 744 is connected between the output of the SR-latch743 and ground.

Referring to FIG. 11B, the SR-latch 743 includes inverter 745, and NANDgates 746 and 747. The BRx signal is fed into the traditional Set input,the Recovery Request signal is fed into the inverted Reset input, and Qoutput provides the output signal c of the SR-latch 743. The inverter745 inverts the Recovery Request signal. The NAND gate 746 performs aNAND operation on the BRx signal and the output of the NAND gate 747,and the NAND gate 747 performs a NAND operation on the inverted RecoveryRequest signal and the output of the NAND gate 746. The output of theNAND gate 746 provides the Q output of the SR-latch 743.

Table 7 describes the function of the output signal c portion of theabc-encoder 743, according to a representative embodiment:

TABLE 7 BRx RR c Amplifier Condition 0 0 1 Boost Request 1 0 1 Satisfied1 1 0 Recovery Request 1 0 0 Satisfied

Table 7 shows that a boost request results in a 1 at the output of theabc-encoder 743, and the 1 persists until a recovery request isasserted. The output goes to 0 for a recovery request, and the 0persists until a boost request is asserted. So, the output signal c ofthe SR-latch 743 is a one-bit word that corresponds to the last eventrequest made by the power amplifier 110.

All together the abc-encoder produces a three-bit word that describesthe last event request made by the power amplifier 110, together withthe state of the DC controller 130 at the time the request was asserted.This is sufficient information for the DC controller 130 to determinewhat action to take. For example, if the power amplifier 110 requests aboost event (via Boost Request signal) and the DC controller 130 is instate 1 at the time of the boost request, the DC controller 130 willchange to state 2. If the DC controller 130 is in state 3 at the time ofthe request, the DC controller 130 will take no action. If the poweramplifier 110 requests a recovery event (via Recovery Request signal)and the DC controller 130 is in state 2 at the time of the recoveryrequest, the DC controller will change to state 1. If the DC controller130 is in state 1 at the time of the recovery request, the DC controller130 will take no action. The logic that facilitates these responses willbe described later, but for now it is sufficient to see that theabc-encoder 740 provides all of the necessary information for the DCcontroller 130 to take the correct action. These results are summarizedin Table 8 below:

TABLE 8 a b c Request Time State Request Action 0 0 0 State 1 RecoveryRemain in State 1 0 0 1 State 1 Boost Switch to State 2 1 0 0 State 2Recovery Switch to State 1 1 0 1 State 2 Boost Switch to State 3 1 1 0State 3 Recovery Switch to State 2 1 1 1 State 3 Boost Remain in State 3

FIG. 12 is a circuit diagram of the w-encoder 750 of the switchsequencer 420, according to a representative embodiment. Generally, thepurpose of the w-encoder 750 is to facilitate boost lockout when acapacitor discharge fault is detected. This is accomplished by receivingEnable signal from the fault recovery circuit 440, which is normally setto a value of 0 when no fault is present.

Referring to FIG. 12, the w-encoder 750 performs a pass-throughoperation and a gate signal generation operation. The pass-throughoperation is performed by inverters 751 to 753 and NOR gates 754 to 756.The inverters 751, 752 and 753 are configured to invert output signalsa, b and c, and to provide at their outputs inverted signals ab, bb, andcb, respectively. The NOR gates 754, 755 and 756 are configured toperform NOR operations on the inverted signals ab, bb and cb and theEnable signal, respectively, to provide the output signals w1, w2 andw3, respectively. The gate signal operation is performed by NOR gates781 to 788. The NOR gates 781, 782, 785 and 786 are each configured toperform NOR operations on the output signals a, b and c, and theinverted signals ab, bb, and cb, in specific combinations, as shown. TheNOR gate 783 is configured to perform a NOR operation on the output ofthe NOR gates 781 and 782, and the NOR gate 787 is configured to performa NOR operation on the output of the NOR gates 785 and 786. The NOR gate784 is configured to perform a NOR operation on the output of the NORgate 783 and the Enable signal to provide the Gate2 signal, and the NORgate 788 is configured to perform a NOR operation on the output of theNOR gate 787 and the Enable signal to provide the Gate3 signal.

According to the pass-through operation, the Enable signal is equal to 0and the output signals a, b and c (the abc word) provided by theabc-encoder 740 are passed through as the output signals w1, w2 and w3,respectively, under a no fault condition. If a fault exists, the Enablesignal is equal to 1, which will lock out the output signals a, b and cfrom passing the NOR gates 754, 755 and 756, and thus the output signalsw1, w2 and w3 will be 0. From Table 8, above, it can be seen that the DCcontroller 130 will assume and maintain state 1 until the faultcondition is alleviated and the Enable signal returns to 0. The abc word0,0,0 may be referred to as the reset state.

The gate signal generation operation is discussed in the context of thefault recovery operation, described below. FIG. 13A is a logic circuitdiagram of the fault recovery circuit 440 of the DC controller 130,according to a representative embodiment. FIG. 13B is a circuit diagramof a slow rise NOR gate of the fault recovery circuit 440 of the DCcontroller 130, according to a representative embodiment. FIG. 13C is acircuit diagram of a slow fall inverter of the fault recovery circuit440 of the DC controller 130, according to a representative embodiment.

Referring to FIG. 13A, the fault recovery circuit 440 includes inverters1321 and 1322 connected in series for processing/buffering the Gate3signal, and inverters 1331 and 1332 connected in series forprocessing/buffering the Gate2 signal. A voltage divider comprisingresistors 1311 and 1312 divides the DC supply voltage Vdc appearing atthe input port In into a sampled DC supply voltage. A second voltagedivider comprising resistors 1313 to 1315 divides the battery voltageVbat into first and second reference voltages, where the secondreference voltage is less than the first reference voltage. A firstcomparator 1325 compares the sampled DC supply voltage and the firstreference voltage, and a second comparator 1335 compares the sampled DCsupply voltage and the second reference voltage, as discussed below.

The fault recovery circuit 440 further includes NAND gate 1323 forperforming a NAND operation on the outputs of the inverter 1322 and thecomparator 1325, and NAND gate 1333 for performing a NAND operation onthe outputs of the inverter 1332 and the comparator 1335. Inverters 1324and 1334 invert the outputs of the NAND gates 1323 and 1333,respectively. Slow rise NOR gate 1340 performs a NOR operation on theoutputs of the inverters 1324 and 1334. An output of the slow rise NORgate 1340 is inverted by inverter 1348, the output of which provides theEnable signal.

Generally, a fault is defined as an excessive discharge of one or bothof the first and second charge storage capacitors 811 and 812 of thepower switch 410. If this occurs, it results in improper operation ofthe DC controller 130. The remedy is to lock out the boost states for aperiod of time sufficient to achieve a complete recharge of the firstand second charge storage capacitors 811 and 812. The fault recoverycircuit 440 facilitates this remedy by detecting the fault and thenasserting Enable signal equal to 1 to the w-encoder 750, as describedabove.

Two types of possible faults are a total charge fault and a singlecapacitor charge fault. A total charge fault occurs when the sum of thecharges on the first charge storage capacitor 811 and the second chargestorage capacitor 812 of the power switch 410 falls below a criticalvalue, resulting in a low state 3 output voltage. This condition isdetected by the comparator 1325, which compares the sampled DC supplyvoltage with the first reference voltage, as mentioned above. The ratioof resistor 1311 and resistor 1312 is chosen to bring the sampled DCsupply voltage into the operating range of the comparator 1325. Valuesof the resistors 1313, 1314 and 1315 are chosen to set the firstreference voltage for the comparator 1325, so that the comparator 1325switches at a predetermined value of the DC supply voltage Vdc output bythe DC controller 130 when state 3 is active. This value may be about 90percent of normal, for instance. To ensure that the decision of thecomparator 1325 passes to the Enable signal output only when state 3 isactive, the Gate3 signal from the w-encoder 750 is used to enable theNAND gate 1323, such that the Gate3 signal is equal to 1 only duringstate 3.

It is also possible for a single capacitor charge fault to impact state2 adversely. This occurs when one of the first and second charge storagecapacitors 811 and 812 being used to produce state 2 has low charge. Todetect this condition, the comparator 1335 also monitors the DC supplyvoltage Vdc output by the DC controller 130 via the sampled DC supplyvoltage by comparing the sampled DC supply voltage with the secondreference voltage. The output of the comparator 1335 passes to theEnable signal output only when Gate2 is equal to 1, where the Gate2signal is also supplied from the w-encoder 750. The Gate2 signal is 1only when state 2 is active. Values of the resistors 1313, 1314 and 1315are chosen also to provide the second reference voltage (lower than thefirst reference voltage) to the comparator 1335, so that the DC supplyvoltage Vdc output by the DC controller 130 in state 2 will switch thecomparator 1335 when the DC supply voltage Vdc drops below apredetermined value. In this case the predetermined value may be about90 percent of normal state 2 output voltage, for instance. To ensurethat the decision of comparator 1335 passes to the Enable signal outputonly when state 2 is active, the Gate2 signal from the w-encoder 750 isused to enable the NAND gate 1333, such that the Gate2 signal is equalto 1 only during state 2. Again the DC controller 130 will be forcedinto state 1 for recharging.

When a fault is generated, the NOR gate 1340 asserts a 0 and the Enablesignal is 1. Referring to FIG. 13B, the NOR gate 1340 may be constructedwith resistor 1345 and capacitor 1346, so that its return to 1 is set bythe time constant formed by the resistor 1345 and the capacitor 1346.The time constant is selected to be long enough to enable recharging ofthe first and second charge storage capacitors 811 and 812 of the powerswitch 410 to take place. In one example, this time is approximately 10μsec. The NOR gate 1340 further includes transistors 1341 and 1344 gatedto the output of the inverter 1324, and transistors 1342 and 1343 gatedto the output of the inverter 1334. In the depicted embodiment, thetransistors 1341 and 1342 are PMOS FETs and the transistors 1343 and1344 and NMOS FETs. The resistor 1345 is connected between the source ofthe transistor 1342 and the drains of the transistors 1343 and 1344(which are connected in parallel to ground). The capacitor 1346 isconnected between the drain of the transistor 1344 and ground, where thedrain of the transistor 1344 is the output Q of the NOR gate 1340.

In addition, as long as the Enable signal remains equal to 1, the gatesignals Gate2 and Gate3 are forced to 0, as can be seen in FIG. 12,where the Enable signal is input to the NOR gates 784 and 788. This gatelockout condition is provided to ensure that fault recovery isterminated after the aforementioned time constant, and that nointervening detection of a fault condition is able to reset this timeperiod during fault recovery.

Inverters 1321 and 1331 are of the slow fall type. Referring to FIG.13C, which depicts an example of inverter 1321 (although the discussionapplies equally to inverter 1331), the slow fall inverter provides timefor the system to stabilize in state 1 before a fault condition isassessed by the fault recovery circuit 440. The inverter 1321 includestransistors 1325 and 1326, which are gated to the output of the seriesconnected inverter 1321. In the depicted embodiment, the transistors1325 is a PMOS FET and the transistor 1326 is an NMOS FET. The resistor1327 is connected between the source of the transistor 1325 and thedrain of the transistor 1326. The capacitor 1328 is connected to thesource of the transistor 1325, and is connected to ground in parallelwith the resistor 1327 and the transistor 1326. The output of theinverter 1321 is at the source of the transistor 1325.

Referring again to FIG. 12, the Gate2 signal and the Gate3 signal arecreated by decoding the abc word to detect the state 2 and state 3conditions, respectively. The input a, b and c signals (bits) are usedto generate ab, bb, and cb inverse bit signals by inverting the a, b andc signals through the 751, 752 and 753, respectively. It can be seen befrom FIG. 12 that the Gate2 and Gate3 signals observe logical equations(11) and (12), where Enableb is the logical inverse of the Enablesignal:Gate2=(ab*bb*c+a*b*cb)*Enableb  (11)Gate3=(a*bb*c+a*b*c)*Enableb  (12)

Based on Equations (11) and (12) and Table 8, the following Table 9truth table for the w-encoder 750 is generated:

TABLE 9 Resultant DC a b c Enable w1 w2 w3 gate2 gate3 Controller State0 0 0 0 0 0 0 0 0 1 0 0 1 0 0 0 1 1 0 2 1 0 0 0 1 0 0 0 0 1 1 0 1 0 1 01 0 1 3 1 1 0 0 1 1 0 1 0 2 1 1 1 0 1 1 1 0 1 3 0 0 0 1 0 0 0 0 0 1 0 01 1 0 0 0 0 0 1 1 0 0 1 0 0 0 0 0 1 1 0 1 1 0 0 0 0 0 1 1 1 0 1 0 0 0 00 1 1 1 1 1 0 0 0 0 0 1

Referring again to FIG. 7, the switch sequencer 420 also includescompensation decoder 770. The compensation decoder 770 is configured todecode the output signals w1, w2 and w3 output by the w-encoder 750 intofirst compensation signal Comp1 and second compensation signal Comp2.The first compensation signal Comp1 is used to drive a firstcompensation switch (e.g., compensation feedback switch 240) and thesecond compensation signal Comp2 is used to drive a second compensationswitch (e.g., compensation feedback switch 250) of the compensationcontrol circuit 200, discussed above. That is, the compensation feedbackswitch 240 is activated to an on state when the first compensationsignal Comp1 is logic high, and the compensation feedback switch 250 isactivated to an on state when the second compensation signal Comp2 islogic high. Table 10 is a truth table describing the desired behavior ofthe first and second compensation signals in the present example:

TABLE 10 State Comp1 Comp2 state 1 0 0 state 2 1 0 state 3 1 1

Due to causality constraints, the control logic obtains the statecondition before the DC supply voltage Vdc output by the DC controller130 settles to the corresponding voltage. It is desirable to derive thefirst and second compensation signals Comp1 and Comp2 from the controllogic rather than from the DC supply voltage Vdc because this providesadvance notice and will give the compensation feedback switches 240 and250 time to settle in synchronicity with voltage changes applied to theoutput transistor 118 of the power amplifier 110. Accordingly, thecompensation decoder 770 operates from the w1, w2, w3 output signal bus,as shown in FIG. 7.

FIG. 14 is a logic circuit diagram of the compensation decoder 770 ofthe switch sequencer 420, according to a representative embodiment.

Referring to FIG. 14, the compensation decoder 770 includes inverters1401 to 1408 and NOR gates 1411 to 1414. Inverters 1402 and 1404 invertthe output signal w1, inverters 1403 inverts the output signal w2, andinverters 1401 and 1405 invert the output signal w3 output by thew-encoder 750. The NOR gate 1411 performs a NOR operation on the outputsignal w2 and the output of the inverter 1401. The NOR gate 1412performs a NOR operation on the outputs of the inverters 1402 and 1403.The NOR gate 1413 performs a NOR operation on the outputs of theinverters 1404 and 1405. The NOR gate 1414 performs a NOR operation onthe outputs of the NOR gates 1411, 1412 and 1413. The inverter 1406inverts the output of the NOR gate 1414 to provide the firstcompensation signal Comp1. The inverters 1407 and 1408 serially invertthe output of the NOR gate 1413 to provide the second compensationsignal Comp2.

The relationships provided by Equations (13) and (14) are observable forthe compensation decoder 770:Comp1=w2b*w3+w1*w2+w1*w3  (13)Comp2=w1*w3  (14)

Referencing Table 9 above, it can be demonstrated that the relations ofthe first and second compensation signals Comp1 and Comp2 satisfy thedesired compensation behavior summarized in Table 10.

What remains is to decode the w bus output of the w-encoder 750 into thefive-bit driver bit bus that will drive the power switch 410. Thisoperation is accomplished by the driver decoder 760.

FIG. 15 is a block diagram of the driver decoder 760 of the switchsequencer 420, according to a representative embodiment. The driverdecoder 760 has three separate functions. The first function is toproduce the codes needed to put the power switch 410 into each of thefour desired states so that the three values of the DC supply voltageVdc are obtained. The second function is to determine which of the firstand second charge storage capacitors 811 and 812 has the greatestcharge, and to insure that the determined one of the first and secondcharge storage capacitors 811 and 812 is used in the next state 2occurrence by adjusting the state 2 control bit word accordingly. Thethird function is to produce the bit changes that result in the desiredcontrol bit word in a specific order that prevents shoot through currentfrom occurring in the power switch 410.

Referring to FIG. 15, the driver decoder 760 includes d-encoder 1510,charge manager 1520, n-sequencer 1530 and p-sequencer 1540. Thed-encoder 1510 is configured to receive the output signals w1, w2 and w3from the w-encoder 750, and to output driver bits d1, d2, d3 and d4. Thecharge manager 1520 is configured to receive the mid-capacitor voltageVmcap from by the power switch 410 at input port In2 and clock signalS1clk from by the S1clk encoder 730, and to output nn signal. Thep-sequencer 1540 is configured to receive the driver bits d1, d2 and d3from the d-encoder 1510, and to output driver bits Vc1 p, Vc4 p and Vc5p. The n-sequencer 1530 is configured to receive the driver bits d2, d3and d4 from the d-encoder 1510, and to output driver bits Vc1 n, Vc2 n,Vc3 n and Vc4 n. The driver decoder 760 further includes 2-to-1multiplexers 550A to 550E which output first through fifth control bitsVc1 to Vc5, respectively. Each of the multiplexers 550A to 550E hassubstantially the same configurations, but receives different inputsignals, as discussed below.

FIG. 16 is a logic circuit diagram of the d-encoder 1510 of the driverdecoder 760, according to a representative embodiment. The d-encoder1510 takes the w bus (providing the output signals w1, w2 and w3) andderives from it a four-bit word comprising the driver bits d1, d2, d3and d4, that is suitable for switching the power switch 410 into itsthree voltages. Notably, the output signals w1, w2 and w3 are invertedby inverters 1631, 1632 and 1633 to provide inverted output signals w1b, w2 b and w3 b.

The d-encoder 1510 includes NOR gates 1601 to 1613 and inverters 1621 to1604. The NOR gate 1601 performs a NOR operation on the output signal w1and inverted output signal w2 b. The NOR gate 1602 performs a NORoperation on the output signals w2 and w3. The NOR gate 1603 performs aNOR operation on the inverted output signal w1 b and output signal w3.The NOR gate 1604 performs a NOR operation on the output signal w1 andground. The NOR gate 1605 performs a NOR operation on the output signalsw1, w2 and inverted output signal w3 b. The NOR gate 1606 performs a NORoperation on the inverted output signals w1 b, w2 b and output signal w3signals. The NOR gate 1607 performs a NOR operation on the outputsignals w1 and w3. The NOR gate 1608 performs a NOR operation on theinverted output signals w2 b and w3 b. The NOR gate 1609 performs a NORoperation on the inverted output signal w1 b and the output signal w2.The NOR gate 1610 performs a NOR operation on outputs of the NOR gates1601 and 1602, and the inverter 1621 inverts the output of the NOR gate1610 to provide the driver bit d3. The NOR gate 1611 performs a NORoperation on outputs of the NOR gates 1603 and 1604, and the inverter1622 inverts the output of the NOR gate 1611 to provide the driver bitd1. The NOR gate 1612 performs a NOR operation on outputs of the NORgates 1605 and 1606, and the inverter 1623 inverts the output of the NORgate 1612 to provide the driver bit d2. The NOR gate 1613 performs a NORoperation on outputs of the NOR gates 1607, 1608 and 1609, and theinverter 1624 inverts the output of the NOR gate 1613 to provide thedriver bit d4.

The relationships provided by Equations (15), (16), (17) and (18) holdfor the d-encoder 1510:d1=w1*w3b+w1b  (15)d2=w1b*w2b*w3+w1*w2*w3b  (16)d3=w1b*w2+w2b*w3b  (17)d4=w1b*w3b+w2*w3+w1*w2b  (18)

Taken together with Table 9 above, truth Table 11 is provided asfollows:

TABLE 11 w1 w2 w3 d1 d2 d3 d4 State 0 0 0 1 0 1 1 1 0 0 1 1 1 0 0 2 1 00 1 0 1 1 1 1 0 1 0 0 0 1 3 1 1 0 1 1 0 0 2 1 1 1 0 0 0 1 3

The driver bits d1 to d4 are then passed into the n-sequencer 1530 andthe p-sequencer 1540, where the same word emerges at the respectiveoutputs of the n-sequencer 1530 and the p-sequencer 1540 afterenforcement of the desired sequence, discussed below in detail. At thispoint, the following relations between the outputs and inputs of then-sequencer 1530 and the p-sequencer 1540 are as follows, once therespective sequences have been enforced:

-   -   Vc1 n=d3    -   Vc2 n=d2    -   Vc3 n=d4    -   Vc4 n=d3    -   Vc5 n=Gnd    -   Vc1 p=d3    -   Vc2 p=Gnd    -   Vc3 p=Vbat    -   Vc4 p=d1    -   Vc5 p=d2

The purpose of the n and p suffixes is to separate the driver bits intothose that generate state 2A and state 2B. Specifically, the n suffixbits are used to enforce state 2A and the p suffix bits enforce state2B. As shown, some driver bits do not require sequencing and are takenfrom Vbat and Gnd. The two sets of driver bits are selected by themultiplexers 550A to 550E.

FIG. 17 is a logic circuit diagram of the multiplexer 550A, according toa representative embodiment. The multiplexers 550B to 550E havesubstantially the same configuration of the multiplexer 550A, except fordifferent input signals resulting in different output signals, as shownin FIG. 15.

Referring to FIG. 17, the representative multiplexer 550A is a 2-to-1multiplexer. The multiplexer 550A includes inverter 1555, which invertsthe nn signal output by the charge manager 1520 to provide pp signal.The multiplexer 550A further includes first and second sets oftransistors. The first set of transistors includes transistor 1551,which is an NMOS FET gated to the nn signal, and transistor 1552, whichis a PMOS FET gated to the pp signal. The second set of transistorsincludes transistor 1553, which is an NMOS FET gated to the pp signal,and transistor 1554, which is a PMOS FET gated to the nn signal. Thesources of the transistors 1551 and 1552 are connected to the p-signalinput to receive the driver bit Vc1 p (from the p-sequencer 1540) andthe drains are connected to the output of the multiplexer 550A. Thesources of the transistors 1552 and 1553 are connected to the n-signalinput to receive driver bit Vc1 n (from the n-sequencer 1530) and thedrains are connected to the output of the multiplexer 550A.

From FIG. 17, it can be seen that when the nn signal is equal to 0, thedriver bit Vc1 n is passed to the output of the multiplexer 550A,whereas when nn signal is equal to 1, the driver bit Vc1 p is passed tothe output of the multiplexer 550A. Generalizing, when the nn signal isequal to 0, the n-signals at the n-signal inputs are passed to theoutputs of the multiplexers 550A to 550E, whereas when nn signal isequal to 1, the p-signals at the p-signal inputs are passed to theoutputs of the multiplexers 550A to 550E.

FIG. 18 is a circuit diagram of the charge manager 1520 of the driverdecoder 760, according to a representative embodiment. The chargemanager 1520 is used to determine which of the first and second chargestorage capacitors 811 and 812 has the most charge, and to assert a 1 or0 value for the nn signal, accordingly. The one of the first and secondcharge storage capacitor 811 and 812 with the most charge is used thenext time state 2 is required.

Referring to FIG. 18, the charge manager 1520 includes a comparator 1521configured to compare the mid-capacitor voltage Vmcap at the fourth node824 (the common node of the first and second charge storage capacitors811 and 812) in the power switch 410 to a voltage divided sampling ofbattery voltage Vbat. The voltage divider includes resistors 1522 and1523, and capacitor 1524 connected in parallel with the resistor 1523.The voltage divider has a voltage gain of about 0.5. When themid-capacitor voltage Vmcap is greater than the reference voltagesupplied by the voltage divider, then the first charge storage capacitor811 has the most charge and a value of 0 is latched by latch 1525 to thenn output as the nn signal when the clock signal S1clk has a positiveedge. When the mid-capacitor voltage Vmcap is less than the referencevoltage, then the second charge storage capacitor 812 has the mostcharge and a value of 1 is latched by the latch 1525 to the nn output asthe nn signal. This determination is made when the power switch 410 isin state 1. For this reason, the clock signal S1clk is configured tohave a rising edge only when the DC controller 130 enters state 1.

FIG. 19 is a circuit diagram of the S1clk-encoder 730 of the switchsequencer 420, according to a representative embodiment.

Referring to FIG. 19, S1clk-encoder 730 includes inverters 731 to 734,NOR gate 735, and capacitors 736 and 737. The inverters 731 and 732serially invert the output x0 from the x-encoder 720, and the inverters733 and 734 serially invert the output x1 from the x-encoder 720. TheNOR gate 735 performs a NOR operation on the outputs of the inverter 732and the inverter 734 to provide the clock signal S1clk output from theS1clk-encoder 730. The capacitor 736 is connected between the output ofthe inverter 731 and ground, and the capacitor 737 is connected betweenthe output of the inverter 733 and ground.

The S1clk-encoder 730 provides a clock signal S1clk having a value of 1at its output only when x0=x1=0, which is the state 1 code for x0, x1.Thus, when the power switch 410 enters state 1, a rising edge of theclock signal S1clk will be generated, and this rising edge will latchthe decision of the comparator 1521 in the charge manager 152 to the nnsignal, as described above.

In view of the foregoing, truth Table 12 for the driver decoder 760 isas follows:

TABLE 12 Q Dominant Desired w1 w2 w3 Capacitor Vc1 Vc2 Vc3 Vc4 Vc5 State0 0 0 811 1 0 1 1 0 1 0 0 0 812 1 0 1 1 0 1 0 0 1 811 0 0 1 1 1 2B 0 0 1812 0 1 0 0 0 2A 1 0 0 811 1 0 1 1 0 1 1 0 0 812 1 0 1 1 0 1 1 0 1 811 00 1 0 0 3 1 0 1 812 0 0 1 0 0 3 1 1 0 811 0 0 1 1 1 2B 1 1 0 812 0 1 0 00 2A 1 1 1 811 0 0 1 0 0 3 1 1 1 812 0 0 1 0 0 3

From Table 12, it can see that the relative charge condition on thefirst and second charge storage capacitors 811 and 812 has the effect ofswitching the power switch 410 between state 2A and state 2B, and has noeffect on state 1 or state 3. A comparison of Table 12 with Table 3 forthe power switch 410 confirms that the states obtained by the powerswitch 410 are the desired states listed in Table 12.

Referring again to FIG. 15, the driver decoder 760 has two sequencers:n-sequencer 1530 and p-sequencer 1540. Together the n-sequencer 1530 andthe p-sequencer 1540 force the driver bit bus (for driver bits d1 to d4)to change state in a constrained sequence that guarantees that the powerswitch 410 is not shorted by a transient overlap of transistor states.In other words, no transient overlap of transistor states is permittedthat would act to either discharge the first or second charge storagecapacitors 811 and 812 or waste energy from the power supply (battery111). To demonstrate this, each of the four states of the power switch410 will be observed, one at a time, from each of the possible previousstates.

FIG. 20 is a circuit diagram of the n-sequencer 1530 of the driverdecoder 760, according to a representative embodiment, and FIG. 21 is acircuit diagram of the p-sequencer 1540 of the driver decoder 760,according to a representative embodiment.

Referring to FIG. 20, n-sequencer 1530 includes four circuits forsequencing driver bits d3, d2, d4 and d3 into driver bits Vc1 n, Vc2 n,Vc3 n and Vc4 n, respectively. The first circuit includes inverter 2001configured to invert the driver bit d3. The first circuit furtherincludes transistors 2011 and 2013 gated to the output of the inventor2001 and transistors 2012 and 2014 gated to the output of the secondcircuit (driver bit Vc2 n). The transistors 2011 and 2012 are PMOS FETsand the transistors 2013 and 2014 are NMOS FETs, although other types oftransistors may be incorporated without departing from the scope of thepresent teachings. The transistor 2011 includes a source connected thebattery voltage Vbat and a drain connected to a source of the transistor2012. The transistor 2012 includes a drain connected to an output forproviding driver bit Vc1 n. Each of the transistor 2013 and thetransistor 2014 includes a drain connected to the output for providingdriver bit Vc1 n and a source connected to ground.

The second circuit includes inverter 2002 configured to invert thedriver bit d2. The second circuit further includes transistors 2021 and2024 gated to the output of the inventor 2002, transistors 2022 and 2025gated to the driver bit d3, and transistor 2023 gated to the output ofthe third circuit (driver bit Vc3 n). The transistors 2021 and 2022 arePMOS FETs and the transistors, 2023, 2024 and 2025 are NMOS FETs,although other types of transistors may be incorporated withoutdeparting from the scope of the present teachings. The transistor 2021includes a source connected the battery voltage Vbat and a drainconnected to a source of the transistor 2022. The transistor 2022includes a drain connected to an output for providing driver bit Vc2 n.The transistor 2023 includes a drain connected to the output forproviding driver bit Vc2 n and a source connected to a drain of thetransistor 2024, which includes a source connected to ground. Thetransistor 2025 includes a drain connected to the output for providingdriver bit Vc2 n and a source connected to ground.

The third circuit includes inverter 2003 configured to invert the driverbit d4. The third circuit further includes transistors 2031 and 2032gated to the output of the inventor 2003, and transistor 2033 gated tothe output of the second circuit (driver bit Vc2 n). The transistor 2031is a PMOS FET and the transistors 2032 and 2033 are NMOS FETs, althoughother types of transistors may be incorporated without departing fromthe scope of the present teachings. The transistor 2031 includes asource connected the battery voltage Vbat and a drain connected to anoutput for providing driver bit Vc3 n. The transistor 2032 includes adrain connected to the output for providing driver bit Vc3 n and asource connected a drain of the transistor 2033. The transistor 2033includes a source connected to ground.

The fourth circuit includes inverter 2004 configured to invert thedriver bit d3. The third circuit further includes transistors 2041 and2042 gated to the output of the inventor 2004, and transistor 2043 gatedto the output of the second circuit (driver bit Vc2 n). The transistor2041 is a PMOS FET and the transistors 2042 and 2043 are NMOS FETs,although other types of transistors may be incorporated withoutdeparting from the scope of the present teachings. The transistor 2041includes a source connected the battery voltage Vbat and a drainconnected to an output for providing driver bit Vc4 n. The transistor2042 includes a drain connected to the output for providing driver bitVc4 n and a source connected a drain of the transistor 2043. Thetransistor 2043 includes a source connected to ground.

Referring to FIG. 21, p-sequencer 1540 includes three circuits forsequencing driver bits d3, d1 and d2 into driver bits Vc1 p, Vc4 p andVc5 p, respectively. The first circuit includes inverter 2101 configuredto invert the driver bit d3. The first circuit further includestransistors 2111 and 2113 gated to the output of the inventor 2101 andtransistors 2112 and 2114 gated to the output of the second circuit(driver bit Vc5 p). The transistors 2111 and 2112 are PMOS FETs and thetransistors 2113 and 2114 are NMOS FETs, although other types oftransistors may be incorporated without departing from the scope of thepresent teachings. The transistor 2111 includes a source connected thebattery voltage Vbat and a drain connected to a source of the transistor2112. The transistor 2112 includes a drain connected to an output forproviding driver bit Vc1 p. Each of the transistor 2113 and thetransistor 2114 includes a drain connected to the output for providingdriver bit Vc1 p and a source connected to ground.

The second circuit includes inverters 2102 and 2104 configured to invertthe driver bit d1 and the output of the second circuit (driver bit Vc5p), respectively. The second circuit further includes transistors 2121and 2123 gated to the output of the inventor 2102 and transistors 2122and 2124 gated to the output of the inverter 2104. The transistors 2121and 2124 are PMOS FETs and the transistors 2122 and 2123 are NMOS FETs,although other types of transistors may be incorporated withoutdeparting from the scope of the present teachings. Each of thetransistors 2121 and 2124 includes a source connected the batteryvoltage Vbat and a drain connected to an output for providing driver bitVc4 p. The transistor 2122 includes a drain connected to the output forproviding the driver bit Vc4 p and a source connected to a drain of thetransistor 2123. The transistor 2123 includes a source connected toground.

The third circuit includes inverter 2103 configured to invert the driverbit d2. The third circuit further includes transistors 2131 and 2134gated to the output of the inventor 2103, transistor 2132 gated to theoutput of the inverter 2104, and transistors 2133 and 2135 gated to thedriver bit d3. The transistors 2131, 2132 and 2133 are PMOS FETs and thetransistors 2134 and 2135 are NMOS FETs, although other types oftransistors may be incorporated without departing from the scope of thepresent teachings. The transistor 2131 includes a source connected thebattery voltage Vbat and a drain connected to a source of the transistor2132. The transistor 2132 includes a drain connected to a source of thetransistor 2133. The transistor 2133 includes a drain connected to anoutput for providing driver bit Vc5 p. Each of the transistors 2134 and2135 includes a drain connected to the output for providing the driverbit Vc5 p and a source connected to ground.

The only previous states possible for state 1 are state 2A and state 2B.The case for the previous state being state 2A will be examined first.Referencing Table 12, state 2A requires control bit word 01000 and state1 requires a control bit word of 10110. This condition corresponds tonn=0. Referencing FIG. 15, the n-sequencer output bus words thatgenerate these two states are shown in Table 13.

TABLE 13 State 2A to State 1 State nn Vc1n Vc2n Vc3n Vc4n 2A 0 0 1 0 0 10 1 0 1 1

Referring to FIG. 18, it can be seen that the n-sequencer 1530 ensuresthat driver bit Vc4 n=1 and driver bit Vc3 n=1, then driver bit Vc2 n=0,then driver bit Vc1 n=1. This means that driver bit Vc5=0, then driverbit Vc4=1 and driver bit Vc3=1, then driver bit Vc2=0, then driver bitVc1=1. The control bit word changes as follows, accordingly. Fifthcontrol bit Vc5 remains 0, then fourth control bit Vc4 changes from 0 to1 and third control bit Vc3 changes from 0 to 1, then second control bitVc2 changes from 1 to 0, then first control bit Vc1 changes from 0 to 1.Referring to FIG. 8, this sequence and the corresponding transistorstates of the power switch 410 are summarized in Table 14 below.

TABLE 14 State 2A to State 1 Previous New Previous New Sequence bitState State Transistor State State 1 Vc5 0 0 805 off off 2 Vc4 0 1 804on off 2 Vc3 0 1 803 on off 3 Vc2 1 0 802 off on 4 Vc1 0 1 801A-C off on

Referring to the FIG. 8 and Table 14, it can be seen that transistorsthat are on to make state 2A are first switched off. Then state 1 isbuilt by switching on first through fourth transistors 801A, 801B, 801Cand 802. The action of switching the fourth transistor 802 on beforeswitching on the others is incidental. The primary objective of theswitch sequencer 420 has been met, in that at no time is the powerswitch 410 shorted by a transient overlap of transistor states.

When referring to FIGS. 20 and 21, as needed, similar analyses result inthe following summary tables for the remaining possible state changes:

TABLE 15 State 2B to State 1 State nn Vc1p Vc4p Vc5p 2B 1 0 1 1 1 1 1 10

TABLE 16 State 2B to State 1 Previous New Previous New Sequence bitState State Transistor State State 1 Vc2 0 0 802 on on 1 Vc3 1 1 803 offoff 1 Vc4 1 1 804 off off 2 Vc5 1 0 805 on off 3 Vc1 0 1 801A-C off on

TABLE 17 State 1 to State 2A State nn Vc1n Vc2n Vc3n Vc4n 1 0 1 0 1 1 2A0 0 1 0 0

TABLE 18 State 1 to State 2A Previous New Previous New Sequence bitState State Transistor State State 1 Vc5 0 0 805 off off 2 Vc1 1 0801A-C on off 3 Vc2 0 1 802 on off 4 Vc4 1 0 804 off on 4 Vc3 1 0 803off on

TABLE 19 State 3 to State 2A State nn Vc1n Vc2n Vc3n Vc4n 3 0 0 0 1 0 2A0 0 1 0 0

TABLE 20 State 3 to State 2A Previous New Previous New Sequence bitState State Transistor State State 1 Vc5 0 0 805 off off 2 Vc1 0 0801A-C off off 3 Vc2 0 1 802 on off 4 Vc4 0 0 804 on on 4 Vc3 1 0 803off on

TABLE 21 State 1 to State 2B State nn Vc1p Vc4p Vc5p 1 1 1 1 0 2B 1 0 11

TABLE 22 State 1 to State 2B Previous New Previous New Sequence bitState State Transistor State State 1 Vc4 1 1 804 off off 1 Vc2 0 0 802on on 1 Vc3 1 1 803 off off 2 Vc1 1 0 801A-C on off 3 Vc5 0 1 805 off on

TABLE 23 State 3 to State 2B State nn Vc1p Vc4p Vc5p 3 1 0 0 0 2B 1 0 11

TABLE 24 State 3 to State 2B Previous New Previous New Sequence bitState State Transistor State State 1 Vc2 0 0 802 on on 1 Vc3 1 1 803 offoff 1 Vc1 0 0 801A-C off off 2 Vc4 0 1 804 on off 3 Vc5 0 1 805 off on

TABLE 25 State 2A to State 3 State nn Vc1n Vc2n Vc3n Vc4n 2A 0 0 1 0 0 30 0 0 1 0

TABLE 26 State 2A to State 3 Previous New Previous New Sequence bitState State Transistor State State 1 Vc4 0 0 804 on on 1 Vc5 0 0 805 offoff 1 Vc1 0 0 801A-C off off 2 Vc3 0 1 803 on off 3 Vc2 1 0 802 off on

TABLE 27 State 2B to State 3 State nn Vc1p Vc4p Vc5p 2B 1 0 1 1 3 1 0 00

TABLE 28 State 2B to State 3 Previous New Previous New Sequence bitState State Transistor State State 1 Vc2 0 0 802 on on 1 Vc3 1 1 803 offoff 1 Vc1 0 0 801A-C off off 2 Vc5 1 0 805 on off 3 Vc4 1 0 804 off on

The switch sequencer 420 may perform a number of subsidiary functions,as well. For example, the switch sequencer 420 may provide state lockand startup lock functions. The state lock function includes holdingeach newly executed state for a minimum dwell time to ensure systemstability. This is especially useful when ringing occurs on output biasand matching network in response to abrupt changes in the batteryvoltage Vbat. The startup lockout function includes holding theamplifier circuit 100 in the first state (e.g., no boost state NB) uponpower up for a time period sufficient to allow complete charge up of thecharge storage capacitors 811 and 812. In addition, as discussed above,the switch sequencer 420 may implement smart logic, which chooses whichof the first or second charge storage capacitors 811 and 82 of the powerswitch 410 to use for intermediate voltage states based on instantaneouscapacitor charge, in order to ensure symmetry of capacitor discharge.

FIG. 22 is a circuit diagram illustrating charge pump voltage source 450of the DC controller 130, according to a representative embodiment. Inan embodiment, the charge pump voltage source 450 provides a charge pumpvoltage Vqp of about 6.3V, for example.

Referring to FIG. 22, the charge pump voltage source 450 includestransistor 940 and transistor 950, which are FETs in the depictedembodiment, although other types of transistors may be incorporatedwithout departing from the scope of the present at teachings. Transistor940 has a drain connected to the voltage source to receive batteryvoltage Vbat and to an anode of diode 960, a source connected to asource of transistor 950, and a gate connected to a gate of thetransistor 950 and a cathode of the diode 960. Transistor 950 has adrain connected to output port 955 for outputting the charge pumpvoltage Vqp. A gate of the transistor 940 is also connected to an outputof NAND gate 930 through a capacitor 914, and a source of the transistor950 is connected to an output of NAND gate 920 through a capacitor 913.

One input of NAND gate 920 is connected to representative seriesinverters 921 and 922, and the other input is connected to the output ofNAND gate 930. Likewise, one input of NAND gate 930 is connected torepresentative series inverters 931 and 932, and the other input isconnected to the output of NAND gate 920. The output of NAND gate 920 isalso connected to the input of the corresponding first inverter 921through resistor 924, and the output of NAND gate 930 is also connectedto the input of the corresponding first inverter 931 through resistor934. Capacitors 911 to 912 are connected between the inputs of inverters921 and 931, respectively, and ground. The resistance values ofresistors 924 and 934, as well as the values of the capacitors 911 toC915, may vary to provide unique benefits for any particular situationor to meet application specific design requirements of variousimplementations, as would be apparent to one skilled in the art.

As can be seen in the depicted representative embodiment, the chargepump voltage source 450 has a simple flip-flop type multi-vibratorfollowed by a voltage doubler, including the NAND gates 920, 930 and thecorresponding inverters 921, 922 and 931, 932. NMOS transistor 940 andPMOS transistor 950 act as rectifiers with essentially zero voltagedrop, hence almost 6.6V (e.g., about 6.3V), for example, can be obtainedfrom a 3.3V supply, such as from the battery 111. Of course, alternativeconfigurations for providing the charge pump voltage Vqp may beincorporated without departing from the scope of the present teachings.

It is understood that the values of various components of the amplifiercircuit 100, including the resistance, capacitance and inductor values,may vary to provide unique benefits for any particular situation or tomeet application specific design requirements of variousimplementations, as would be apparent to one skilled in the art. It isfurther understood that the types of transistors may vary, as discussedabove, and that the sources/drains or the collectors/emitters of thevarious transistors may be reversed, without affecting the relevantfunctionality, depending on design factors of various embodiments.

Accordingly, the supply voltage of the output transistor 118 in thepower amplifier 110 may be selectively boosted, in response to demand onthe power amplifier 110. For example, a no boost voltage Vnb, which isequal to supply voltage Vdd (e.g., battery voltage Vbat), may beinitially provided by the power switch 410 as the collector supplyvoltage. A magnitude of an envelope of the RF input signal Vin receivedby the power amplifier 110 is evaluated by the detector 120 (and thedetector encoder 430) via the corresponding RF output signal Vout, sothat it may be determined when a lowest occurring voltage extreme of theenvelope becomes less than a predetermined boost threshold (e.g., anegative peak voltage level corresponding to saturation voltage of theoutput transistor 118). The power switch 410 then provides a mediumboost voltage Vmb (e.g., 1.5Vdd) as the collector supply voltage of theoutput transistor 118 when the lowest occurring voltage extreme of theenvelope becomes less than the predetermined threshold. The medium boostvoltage Vmb includes the no boost voltage Vnb plus a first voltage boostVb1 (e.g., 0.5Vdd) previously stored in each of the first and secondcharge storage capacitors 811 and 812.

The detector 120 (and the detector encoder 430) continues to evaluatethe magnitude of the envelope of the RF output signal Vout, so that itmay be determined when a lowest occurring voltage extreme of theenvelope becomes less than the predetermined boost threshold. The powerswitch 410 then provides a high boost voltage Vhb (e.g., 2Vdd) as thecollector supply voltage of the output transistor 118 when the lowestoccurring voltage extreme of the envelope becomes less than thepredetermined boost threshold. The high boost voltage Vhb includes theno boost voltage Vnb plus a second voltage boost Vb2 (e.g., Vdd)previously stored in the combined first and second charge storagecapacitors 811 and 812. Also, the detector 120 (and the detector encoder430) may determine when the lowest occurring voltage extreme of theenvelope becomes greater than a predetermined recovery threshold, inresponse to which the power switch 410 steps down, and again providesthe medium boost voltage Vmb or the no boost voltage Vnb as thecollector supply voltage.

The various components, materials, structures and parameters areincluded by way of illustration and example only and not in any limitingsense. In view of this disclosure, those skilled in the art canimplement the present teachings in determining their own applicationsand needed components, materials, structures and equipment to implementthese applications, while remaining within the scope of the appendedclaims.

The invention claimed is:
 1. A control device configured to provide asupply voltage to an output transistor of a power amplifier configuredto amplify an input signal, the control device comprising: a detectorencoder configured to receive a detection signal indicating a negativepeak voltage level of an output signal of the power amplifier, toreceive a reference signal indicating a critical voltage of thedetection signal at which the negative peak voltage level of the outputtransistor is deemed to be out of voltage with reference to saturationvoltage of the output transistor, to compare the detection signal andthe reference signal, and to output a Boost Request signal and aRecovery Request signal in response to the comparison; a switchsequencer configured to translate the Boost Request signal and theRecovery Request signal into a plurality of control bits; and a powerswitch configured to coordinate switching among a no boost voltage and aplurality of different boost voltages based on the plurality of controlbits, and to output one of the no boost voltage and the plurality ofdifferent boost voltages as the supply voltage to the output transistor.2. The control device of claim 1, wherein the power switch comprises aplurality of charge storage capacitors selectively connectable to anoutput of the control device under control of the plurality of controlbits from the switch sequencer to enable outputting the supply voltage.3. The control device of claim 2, wherein the power switch furthercomprises a plurality of transistors controlled by the plurality ofcontrol bits to selectively connect the plurality of charge storagecapacitors to the output of the control device.
 4. The control device ofclaim 2, wherein the plurality of control bits prevent each of theplurality of charge storage capacitors from being shorted by the powerswitch.
 5. The control device of claim 1, wherein the plurality ofcontrol bits comprise a two bit word, the first bit providing the BoostRequest signal and the second bit providing the Recovery Request signal.6. The control device of claim 5, wherein when the detection signalfalls below the reference signal, indicating the negative peak voltagelevel of the output transistor falls below the saturation voltage of theoutput transistor, the Boost Request signal triggers a boost event forstepping up to a higher boost voltage of the plurality of boostvoltages.
 7. The control device of claim 5, wherein when a scaleddetection signal of the detection signal is above a scaled referencesignal of the reference signal, indicating the negative peak voltagelevel of the output transistor is above the saturation voltage of theoutput transistor, the Recover Request signal triggers a recovery eventfor stepping down to a lower boost voltage of the plurality of boostvoltages or a no boost voltage.
 8. The control device of claim 1,wherein the plurality of boost voltages comprise a medium boost voltageand a high boost voltage.
 9. The control device of claim 1, wherein thedetector encoder comprises: a first comparator configured to compare thedetection signal and the reference signal to output the Boost Requestsignal; and a second comparator configured to compare a scaled detectionsignal and a scaled reference signal to output the Recovery Requestsignal, wherein the scaled detection signal is based on dividing thedetection signal down by a divider ratio, and the scaled referencesignal is based on dividing the reference signal to provide a scaledreference signal and adding an offset voltage to the scaled referencesignal.
 10. The control device of claim 1, further comprising: a chargepump power supply configured to provide a charge pump voltage to thepower switch to charge at least one of the plurality of charge storagecapacitors to a voltage approximately equal to the supply voltage. 11.The control device of claim 2, further comprising: a fault recoverycircuit configured to detect a fault in the supply voltage output by thecontrol device, and based on detection of the fault, to output an Enablesignal to selectively enable operation of the switch sequencer and todisable the plurality of boost voltages.
 12. The control device of claim11, wherein the fault refers to an insufficiency in at least one of theboost voltages as a result of excessive discharge of at least one of theplurality of charge storage capacitors of the power switch.
 13. Thecontrol device of claim 12, wherein the fault recovery circuit disablesthe plurality of boost voltages for a time period sufficient to permitthe at least one of the plurality of charge storage capacitors havingexcessive discharge to fully recharge.
 14. The control device of claim3, wherein each switch of the plurality of switches comprises a fieldeffect transistor (FET).
 15. The control device of claim 1, wherein thedetector encoder is further configured to generate at least onecompensation signal for providing feedback compensation and quiescentbias compensation to the output transistor.
 16. The control device ofclaim 15, wherein n−1 compensation signals are generated, n being thenumber of different supply voltages able to be produced by the controldevice, wherein n is an integer greater than one.
 17. A device forcontrolling operation of an amplifier having an output transistor, thedevice comprising: a detector configured to detect a negative peakvoltage level of an output signal of the amplifier and to generate acorresponding detection signal; and a controller configured to provide asupply voltage to the output transistor of the power amplifier based ona comparison of the detection signal and a reference signal, thereference signal indicating a critical voltage for the detection signalat which the output transistor is deemed to be out of voltage and inneed of a voltage boost, the supply voltage comprising one of a no boostvoltage or one of a plurality of stepped boosted voltages, wherein thesupply voltage provided by the controller is one of the no boost voltageor a stepped boosted voltage less than a current supply voltage when thedetection signal is less than the reference signal, and is one of theplurality of stepped boosted voltages when the detection signal isgreater than the reference signal.
 18. The device of claim 17, whereinthe critical voltage corresponds to saturation of the output transistor.19. The device of claim 18, wherein the detector detects the negativepeak voltage level by evaluating a magnitude of an envelope of theoutput signal.
 20. The device of claim 17, further comprising: acompensation circuit connected as shunt feedback around the outputtransistor of the amplifier, and configured to receive a plurality ofcompensation signals generated by the controller for compensating forchanges in magnitude and phase when the supply voltage provided by thecontroller is increased.